- Updated `import_string` to evict conflicting cached top-level plugin packages, ensuring proper isolation of plugins with the same package names.
- Preserved the order of legacy handler declarations in `_iter_discoverable_names` to maintain expected behavior for legacy plugins.
- Added tests to verify the isolation of top-level packages and the preservation of handler declaration order.
- Improved module cleanup in tests to prevent conflicts between plugins.
- Introduced LoadedCapability class to manage plugin capabilities.
- Updated load_plugin function to discover and load capabilities alongside handlers.
- Enhanced Peer class to handle remote provided capabilities during initialization.
- Added tests for capability registration and invocation in legacy plugins.
- Improved MessageChain and message component handling in legacy plugins.
- Added comprehensive tests for legacy plugin integration and compatibility.
- Updated protocol messages to include provided capabilities in initialization.
- Enhanced top-level module imports to include capability-related functions.
