feat: Expand safe directory traversal to all Unix platforms and fix related type conversions. #15530

Job	Run time
Style/spelling (ubuntu-latest, feat_os_unix)	17s
Style/format (ubuntu-latest, feat_os_unix)	11s
Pre-commit hooks	34s
Style/Python	8s
Style/toml	14s
Style/lint (ubuntu-latest, all, true)	1m 35s
Style/lint (windows-latest, feat_os_windows)	2m 12s
Style/lint (macos-latest, feat_os_macos)	2m 46s
	7m 57s

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