iceberg: support views (#10069)

* s3tables: tag table entries and exclude views from table listings

* s3tables: add view CRUD operations

* iceberg: support view create, load, exists, drop, and list

* iceberg: support view update

* iceberg: test view error classification and metadata round-trip

* iceberg: pre-check existence and write view metadata only after create

* iceberg: map view namespace-not-found to 404

* iceberg: test view create namespace-404 and duplicate no-clobber

* s3tables: tag view metadata and entry type atomically

CreateView wrote ExtendedKeyMetadata and ExtendedKeyEntryType in two
UpdateEntry calls, so a partial failure could leave a view directory
untagged. Add setExtendedAttributes to set both in one UpdateEntry.

* iceberg: roll back view registration when metadata write fails

The metadata file is written after the catalog registers the view. If
that write fails, drop the just-created view so it doesn't linger
pointing at a missing metadata.json. Reuse the DeleteView path via a
shared dropView helper.

weed/s3api/s3tables/handler_view_test.go

@@ -0,0 +1,33 @@
+package s3tables
+
+import "testing"
+
+func TestEntryType(t *testing.T) {
+	cases := []struct {
+		name     string
+		extended map[string][]byte
+		want     string
+	}{
+		{"nil extended is table", nil, EntryTypeTable},
+		{"absent marker is table", map[string][]byte{ExtendedKeyMetadata: []byte("{}")}, EntryTypeTable},
+		{"empty marker is table", map[string][]byte{ExtendedKeyEntryType: {}}, EntryTypeTable},
+		{"table marker", map[string][]byte{ExtendedKeyEntryType: []byte(EntryTypeTable)}, EntryTypeTable},
+		{"view marker", map[string][]byte{ExtendedKeyEntryType: []byte(EntryTypeView)}, EntryTypeView},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			if got := entryType(c.extended); got != c.want {
+				t.Fatalf("entryType() = %q, want %q", got, c.want)
+			}
+		})
+	}
+}
+
+func TestGenerateViewARN(t *testing.T) {
+	h := NewS3TablesHandler()
+	got := h.generateViewARN(DefaultAccountID, "warehouse", "ns/v")
+	want := "arn:aws:s3tables:us-east-1:000000000000:bucket/warehouse/view/ns/v"
+	if got != want {
+		t.Fatalf("generateViewARN() = %q, want %q", got, want)
+	}
+}