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

src/core/widgets/code/command_system/commands/dnd_load_file_to_buffer.py

@@ -9,6 +9,7 @@ from gi.repository import GtkSource
 from gi.repository import Gtk
 from gi.repository import Gdk
 from gi.repository import Gio
+from gi.repository import GLib
 
 # Application imports
 from ..command_helpers import update_info_bar_if_focused
@@ -35,6 +36,10 @@ def execute(
     update_info_bar_if_focused(view.command, view)
     view.emit("focus-in-event", Gdk.Event())
 
-    buffer = view.get_buffer()
-    itr    = buffer.get_iter_at_mark( buffer.get_insert() )
-    view.scroll_to_iter(itr, 0.2, False, 0, 0)
+    def scroll_to_insert_itr(view):
+        buffer = view.get_buffer()
+        itr    = buffer.get_iter_at_mark( buffer.get_insert() )
+        view.scroll_to_iter(itr, 0.2, False, 0, 0)
+
+    GLib.idle_add(scroll_to_insert_itr, view)
+