ci: clean up stale FUSE mounts before running tests (#12020)

* ci(s3tables): tolerate stale FUSE mounts in disk diagnostics

* ci(s3tables): bound df diagnostics with timeout, explain once

A stale FUSE mount can also hang statfs, not just fail it, so wrap df in
timeout 15; one comment at the first site covers all sixteen.

* ci: tolerate stale FUSE mounts in df diagnostics elsewhere

The same self-hosted runners serve the other workflow files; a bare
df -h there can stall or fail a job the same way.

* ci: unmount disconnected FUSE test mounts before jobs start

* ci: skip FUSE cleanup when the variant checkout is skipped

* ci: reclaim the crashed run's test dir once its stale FUSE mount is detached

* ci: stop tracking python bytecode for the FUSE cleanup action

The helper's __pycache__ slipped into the tree; ignore it so local
test runs cannot re-add it.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* ci: run the FUSE cleanup action's unit tests on action changes

test_cleanup.py was never wired into CI, so a regression in cleanup.py
would ship silently. A path-filtered workflow runs it on every change
under .github/actions/.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* ci: match every FUSE test mount layout in the cleanup action

The candidates list only matched seaweedfs_fuse_test_*/mount, so stale
mounts left by fuse_failover and fuse_p2p runs (mountN leaves under
seaweedfs_fuse_* dirs) and the posix-compliance workflow's fixed
/tmp/seaweedfs/mount were never reclaimed and could still wedge df.

* ci: run the FUSE mount cleanup in the fuse_failover and fuse_p2p workflows

---------

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

.github/workflows/fuse-failover.yml

@@ -42,6 +42,9 @@ jobs:
         with:
           persist-credentials: false
 
+      - name: Clean up stale FUSE mounts
+        uses: ./.github/actions/cleanup-stale-fuse-mounts
+
       - name: Set up Go
         uses: actions/setup-go@v7
         with: