CHANGES: Add fixture cache and file_lock entries (#502)

Author: tony

CHANGES

@@ -18,7 +18,21 @@ $ uv add libvcs --prerelease allow
 
 <!-- Maintainers, insert changes / features for the next release here -->
 
-_Upcoming changes will be written here._
+### pytest plugin
+
+#### pytest_plugin: Add XDG persistent cache for fixtures (#502)
+
+- Add XDG-based persistent cache at `~/.cache/libvcs/pytest/`
+- Add {class}`~libvcs.pytest_plugin.RepoFixtureResult` with cache hit/miss tracking
+- Add atomic initialization for pytest-xdist compatibility
+- Significantly faster test runs when cache is warm
+
+### Internal
+
+#### _internal: Add file locking module (#502)
+
+- Add {class}`~libvcs._internal.file_lock.FileLock` for cross-platform file locking
+- Add {func}`~libvcs._internal.file_lock.atomic_init` for race-free initialization
 
 ### Development