- Added `pluginSchedulerState` interface with `HasScheduler` method for improved plugin scheduler state checks.
- Updated `Manager.hasPluginScheduler` to handle `HasScheduler` logic.
- Implemented and tested fast-path handling for inactive plugin schedulers, including mixed provider scenarios.
- Expanded unit test coverage to ensure correct behavior in various scheduler states.
- Added a Go scheduler plugin demonstrating CLIProxyAPI capabilities, such as `plugin.register`, `plugin.reconfigure`, and `scheduler.pick`.
- Implemented methods for plugin configuration, built-in scheduler delegation (`fill-first`, `round-robin`), dynamic candidate selection, and error handling.
- Extended `pluginhost` with scheduler handling, candidate normalization, and fallback mechanisms.
- Included examples, tests, and detailed documentation for scheduler usage and implementation.
