Add metadataEqualIgnoringTimestamps() function to compare metadata JSON
without timestamp/expired/expires_in/last_refresh/access_token fields.
This prevents unnecessary file writes when only these fields change
during refresh, breaking the fsnotify event → Watcher callback → refresh loop.
Key insight: Google OAuth returns a new access_token on each refresh,
which was causing file writes and triggering the refresh loop.
Fixes antigravity channel excessive log generation issue.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
- Replaced `TokenRecord` with `coreauth.Auth` for centralized and consistent authentication data structures.
- Migrated `TokenStore` interface to `coreauth.Store` for alignment with core CLIProxy authentication.
- Updated related login methods, token persistence logic, and file storage handling to use the new `coreauth.Auth` model.
- Removed `FileStore` in favor of the new `FileTokenStore`.
- Centralized auth JSON handling and token operations through `FileTokenStore`.
- Updated all components to utilize `FileTokenStore` for consistent storage operations.
- Introduced `SetBaseDir` and directory locking mechanisms for flexible configurations.
- Enhanced metadata management, including path resolution and deep JSON comparisons.
