fix(catalog): avoid redundant hadoop namespace stat

[gitcommit90]

Summary

Remove the standalone Stat call before WalkDir in the Hadoop catalog's DropNamespace path.

WalkDir already reports a missing root path, so the separate pre-check widens a check-to-use race window where another caller can delete or recreate the namespace between the two filesystem calls.

Changes

• Rely on WalkDir for missing namespace detection
• Preserve existing behavior for a namespace path that is a file, not a directory, by checking the root WalkDir entry and returning ErrNoSuchNamespace
• Keep existing WalkDir error handling for missing namespaces and non-empty namespaces

Verification

• go test -v ./catalog/hadoop — pass
• golangci-lint run --timeout=10m ./catalog/hadoop/... — 0 issues
• git diff --check — clean

Fixes #1273

[zeroshade]

LGTM pending CI success

[laskoviymishka]

is this still needed after #1273 and #1293?