fix: close Files.walk stream in GitVersionControlLocalFileStorage.del…

[LakshyaMalik18]

What changes were proposed in this PR?

GitVersionControlLocalFileStorage.deleteRepo called Files.walk(...) without closing the returned stream. Files.walk returns a closeable Stream backed by an open directory handle, so the handle leaked until GC — which can flake temp-dir deletion on Windows and leak file descriptors on long-lived JVMs.

This PR wraps the walk in a try-with-resources block so the stream (and its underlying directory handle) is always closed, even if iteration throws. No behavior change for callers.

Any related issues, documentation, discussions?

Closes #5548

How was this PR tested?

No new tests added. This is a stream-lifecycle fix with no behavior change; existing dataset deletion paths already exercise deleteRepo.

Was this PR authored or co-authored using generative AI tooling?

The code change was taken from the fix described in issue #5548. The PR description was drafted with assistance from Claude (Anthropic).
Generated-by: Claude (Anthropic)

[github-actions]

👋 Thanks for your first contribution to Texera, @LakshyaMalik18!

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