refactor(lsp): restructure lsp plugin controller architecture and simplify provider cache

- Replace LSPManager usage with LSPController integration
- Move UI access through lsp_controller.lsp_manager_ui
- Remove legacy ProviderResponseCache client management
- Simplify completion filtering and matcher handling
- Improve typing annotations and modernize union syntax
- Clean up unused imports and dead code
- Fix completion item parsing for insertText/textEdit fallbacks
- Add async-safe scrolling via GLib.idle_add

plugins/code/ui/lsp_manager/handlers/python.py

@@ -0,0 +1,12 @@
+# Python imports
+
+# Lib imports
+
+# Application imports
+from .default import DefaultHandler
+
+
+
+class PythonHandler(DefaultHandler):
+    """Uses default handling, can override if Python needs special logic."""
+    ...