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/base.py

@@ -0,0 +1,31 @@
+# Python imports
+from abc import ABC
+
+# Lib imports
+
+# Application imports
+
+
+
+class BaseHandler:
+    def __init__(self):
+        self.context        = None
+        self.response_cache = None
+
+
+    def set_context(self, context):
+        self.context = context
+
+    def set_response_cache(self, response_cache):
+        self.response_cache = response_cache
+
+    @property
+    def emit(self):
+        return self.context.emit
+
+    @property
+    def emit_to(self):
+        return self.context.emit_to
+
+    def handle(self, method: str, response, controller):
+        pass