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* Remove legacy handlers system (BaseHandler, DefaultHandler, JavaHandler, PythonHandler, HandlerRegistry) * Introduce response_handlers module with ResponseRegistry for LSP response routing * Replace HandlerRegistry usage in LSPManager with ResponseRegistry * Convert LSPManagerUI client lifecycle to GObject signals * Remove GLib.idle_add usage in LSP client event dispatch * Move completion request logic into LSPServerEventsMixin * Replace provider.py and provider_response_cache.py with modular provider/ package * Simplify plugin wiring via response_registry.set_event_hub() This refactor decouples response handling, simplifies event flow, and prepares the LSP manager for easier language-specific extensions.