rust: clippy-clean both crates and adopt the std APIs the 1.91 MSRV allows (#11312)

* rust: apply clippy --fix to both crates

The mechanical part of a clippy sweep: `cargo clippy --all-targets --fix`
on seaweed-volume and the seaweed-worker workspace, hand-reviewed. Both
manifests declare their MSRV (1.91.1 and 1.94.1), so every suggestion
clippy applied is within it: the collapsible_if sites become let chains
(1.88, edition 2024), `% n == 0` becomes is_multiple_of (1.87),
chunks_exact with a constant becomes as_chunks (1.88), repeat().take()
becomes repeat_n (1.82), and io::Error::new(Other, ..) becomes
io::Error::other (1.74). The rest is redundant clones, borrows, casts,
closures and field names.

Nothing here changes behaviour. The three let_and_return sites in
needle_map.rs and store_ec.rs deserve a note: the `let result = ..;
result` shape was a deliberate edition-2021 workaround to drop a redb
guard before the table it borrows. Edition 2024 drops tail-expression
temporaries before locals, which is why clippy now flags it, and the
two comments that described the workaround say so instead.

Manual edits on top of the tool output: the blocks clippy rewrote are
re-indented the way rustfmt lays them out (only those blocks — the
crate is not rustfmt-clean and a whole-crate fmt would bury this diff),
the blank lines let_and_return left behind are removed, and the CRC
legacy_value test compares against a literal worked out from the
original shift formula rather than restating rotate_right.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CjZY429aVU74SLDmo1wiuU

* rust: clear the clippy warnings --fix cannot apply, and say why the rest stay

Hand fixes for the lints clippy only reports. Behaviour is unchanged
throughout; each rewrite is the one clippy names.

- needless_range_loop (7): index loops over shard vectors become
  iterator loops. Where the old code indexed `v[..n]` the new loop
  iterates `v[..n]` so an undersized vector still panics the same way.
- field_reassign_with_default (6): struct literals with `..Default`.
- redundant_pattern_matching (3): `if let Err(_) = guard.check()` becomes
  `.is_err()`, which also releases the read guard at the end of the
  condition instead of at the end of the block.
- manual_strip (2), manual_checked_ops, format_in_format_args,
  redundant_locals, wrong_self_convention (to_vif takes self by value,
  so it is into_vif; CompactEntry is Copy, so to_needle_value takes self).
- type_complexity (2): `OrphanShardLoad` and `RawNeedleEntry` name two
  tuples that were spelled out inline.
- new_without_default: CompactNeedleMap gets a Default that calls new().
- suspicious_open_options: a test helper spells out `.truncate(false)`,
  which is what `.create(true).write(true)` already did.

What stays, and the attribute that says so:

- too_many_arguments (10): `#[expect]` on each function. Folding 8–15
  parameters into a struct is a design change, not a lint fix.
- await_holding_lock / readonly_write_lock: one test holds the store
  write guard across a sleep on purpose, as a barrier that parks the
  copy task at the mount block. `#[expect(.., reason = ..)]` records it.
- module_inception: needle/needle.rs mirrors the Go package layout.

Two lints become crate-wide policy in `[lints.clippy]`, with the reason
next to each: result_large_err, because every RPC path returns
tonic::Status (176 bytes) and boxing it would change every handler
signature; and needless_update, because `..Default::default()` on a
protobuf message literal is what lets a proto gain a field without
touching every constructor (all 11 sites are pb messages). The worker
workspace gets the same table and its members opt in with
`lints.workspace = true`; its generated plugin.rs also allows
large_enum_variant on prost's oneof enums.

Both crates are now clean under `cargo clippy --all-targets -- -D warnings`.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CjZY429aVU74SLDmo1wiuU

* rust volume: use the std APIs the 1.91 MSRV already pays for

The crate declares rust-version 1.91.1, so a few things the code still
worked around are plain std now. All of them come from the 1.85–1.91
release notes; nothing here needs a newer toolchain than the manifest
already requires.

- std::sync::LazyLock (1.80) replaces the lazy_static! block in
  metrics.rs, and the lazy_static dependency goes. Every use site reads
  the same through Deref, so no caller changes.
- Duration::from_mins / from_hours (1.91) replace `from_secs(v * 60)`
  and `from_secs(v * 3600)` in the option parser and the shard-location
  refresh TTLs. One difference for the parser: an absurd count that
  overflows u64 seconds now panics in release builds too, where the
  multiplication used to wrap.
- Result::flatten (1.89) replaces `.and_then(|r| r)` on the replication
  join handle.
- OsStr::display (1.87) replaces `to_string_lossy()` where the name was
  only being formatted; the output is byte-identical.
- `#[allow]` becomes `#[expect]` (1.81) on the suppressions that are
  meant to be permanent, so a suppression that stops being needed
  becomes a warning rather than lingering. Doing that found four that
  already had: dead_code on ChunkManifest, base_name and last_io_error,
  and too_many_arguments on read_from_data_shards, which is down to
  seven parameters. Those attributes are deleted. The three allows that
  depend on cfg (a unix-only mutation, a linux-only field set, a
  profiling-only parameter) stay as allow, because expect would be
  unfulfilled on the other platforms.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CjZY429aVU74SLDmo1wiuU

* ci: add a commented-out clippy step to both Rust workflows

Both crates are warning-free under `cargo clippy --all-targets
-D warnings` now. Whether that becomes a gate is a policy call, so the
step is present but commented out; uncommenting it is the whole change.
The comment points at the `[lints.clippy]` table where crate-wide
exceptions are recorded, so the gate does not become a reason to
sprinkle allows.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CjZY429aVU74SLDmo1wiuU

* rust volume: guard parse_duration against overflow panics

Duration::from_mins/from_hours panic when the count overflows u64
seconds. Use checked_mul so an oversized CLI value falls back to the
parser default instead of crashing volume startup.

---------

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>
Co-authored-by: Chris Lu <chris.lu@gmail.com>

.github/workflows/rust-worker-tests.yml

@@ -73,6 +73,12 @@ jobs:
       - name: Build the plugin workers
         run: cd seaweed-worker && cargo build --release
 
+      # The workspace is warning-free under clippy as of the sweep that added
+      # this step. Uncomment to make that a gate; `[workspace.lints.clippy]`
+      # in seaweed-worker/Cargo.toml is where crate-wide exceptions live.
+      # - name: Clippy
+      #   run: cd seaweed-worker && cargo clippy --workspace --all-targets -- -D warnings
+
       # The tests that need a live gateway skip themselves without one, the way
       # the Go integration tests skip without Docker; the lifecycle suite in
       # test/s3tables/lifecycle is what runs them against a real cluster.