Fix deleter crash

[JJ9276489]

Fixes #30102

The deleter previously assumed that every entry in log_root was a valid segment directory. Stray files or broken symlinks would accumulate and prevent cleanup from progressing correctly. This change hardens the deletion logic so that unexpected non-directory entries are removed first, and failures are logged rather than crashing the thread.

Changes

• Delete non-directory items in log_root before processing segment directories

• Safely handle failures in os.remove, os.listdir, and shutil.rmtree

• Preserve normal semantics:

  • skip locked segments

  • skip preserved segments

  • delete earliest eligible directory

Verification

A new test, test_delete_mixed_contents, creates a realistic mixed-state log_root containing:

• regular files with segment-style names

• random stray logs

• broken symlinks

• a valid symlink pointing to a real directory tree

• nested directories containing files

• a real segment directory

Before this change, the test failed due to skipped cleanup and unhandled errors.
After this change, the test passes and cleanup proceeds correctly without crashes.

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