Move all rsync-related tests (44 tests) from test_fs.py to new
test_rsync.py module for better organization:
- TestRsync (14 tests)
- TestRsyncBasic (5 tests)
- TestParseRsyncOutput (17 tests)
- TestRsyncExt (8 tests)
Extract shared helper functions to conftest.py to eliminate duplication:
- create_file(), create_dir(), relpath()
- check_identical_file()
- common_fs_dirs fixture
This improves test organization and maintainability by grouping related
tests and removing code duplication between test modules.
