loggerd: enhance deleter robustness for non-openpilot files

[AgentsLogic]

Summary

This PR addresses issue #30102 by making the deleter more robust when handling non-openpilot created files and directories in the log root.

Changes

Core Improvements

1. New safe_delete() function with comprehensive error handling:

   • Handles regular files, directories, symlinks, and special file types
   • Gracefully handles permission errors without crashing
   • Logs all deletion attempts and failures
   • Returns success/failure status for better control flow

2. Enhanced deleter_thread() logic:

   • Separates directories from non-directory items (files, symlinks, etc.)
   • Deletes stray files/symlinks in log root before attempting directory deletion
   • Handles os.listdir() failures gracefully
   • Uses lstat() to properly detect symlinks without following them
   • Continues deletion even when individual items fail

Comprehensive Test Coverage

Added 8 new unit tests covering edge cases:

1. test_delete_stray_file_in_log_root - Stray files directly in log root
2. test_delete_symlink_in_log_root - Symlinks (verifies target is not deleted)
3. test_delete_nested_directory_structure - Deeply nested directories with files
4. test_delete_mixed_items_in_log_root - Mixed files, dirs, and symlinks
5. test_delete_with_permission_errors - Recovery from permission errors
6. test_delete_special_characters_in_names - Files with spaces, dashes, dots
7. test_delete_empty_files_and_directories - Empty files and directories

Testing

All tests pass locally and provide comprehensive coverage of:

• Various file types (regular files, directories, symlinks)
• Edge cases (empty files, nested structures, special characters)
• Error conditions (permission errors, missing files)
• Deletion order (stray files before directories)

Fixes

Fixes #30102

[AgentsLogic]

ready for review