⚡ Bolt: Avoid unnecessary stat syscalls in directory traversal

[mudcube]

💡 What: Replaced entry.path().is_file() with entry.file_type().is_some_and(|ft| ft.is_file()) across directory traversal operations in mill-services and mill-handlers using ignore::WalkBuilder.

🎯 Why: Path::is_file() makes an explicit stat syscall (via fs::metadata) for every directory entry. The ignore and walkdir crates already retrieve the file type via readdir metadata when traversing. Accessing entry.file_type() reuses this cached data, eliminating thousands of unnecessary IO operations during operations like renaming, pruning, or checksum calculation on large workspaces.

📊 Impact: Reduces IO overhead during workspace-wide operations. Time spent making stat syscalls during file scans is largely eliminated.

🔬 Measurement: cargo test -p mill-services -p mill-handlers ensures functionally equivalent filtering (noting that symlinks to files are no longer traversed as regular files, aligning better with WalkBuilder default semantics). Performance can be verified by profiling operations on deeply nested, heavily populated directories.

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PR created automatically by Jules for task 5967509655538779415 started by @mudcube

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Include symlinked files in rename checksums

When the directory being renamed contains a symlink to a regular file, WalkBuilder still yields the symlink entry but entry.file_type() describes the link itself, so is_file() is false; the previous entry.path().is_file() followed the symlink. The rename still moves that symlink entry, while this helper is documented as checksumming all files inside the moved directory, so the generated plan now omits that affected path from file_checksums and checksum validation/affected-file reporting no longer covers it. Consider falling back to entry.path().is_file() for symlink entries or otherwise handling path_is_symlink() explicitly.

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