On Windows, shutil.rmtree() fails when deleting a directory that contains
an open SQLite database file. The ZIP update path in _download_and_replace_zip()
calls _clean_plugin_folder() which tries to delete the cache/ directory,
but downloaded_versions.sqlite is held open by DownloadedVersionHistoryService.
Fix:
- Add close() method to DownloadedVersionHistoryService to release
the persistent SQLite connection
- Call close() before _clean_plugin_folder() in the ZIP update flow
- Add 'cache' to the skip_files list so the runtime cache directory is
never deleted during plugin updates
d02a0611d3