refactor(lsp-manager): replace handler architecture with response registry and modular providers

* 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.

plugins/code/ui/lsp_manager/provider/provider.py

@@ -0,0 +1,85 @@
+# Python imports
+
+# Lib imports
+import gi
+gi.require_version('GtkSource', '4')
+
+from gi.repository import GObject
+from gi.repository import GtkSource
+
+# Application imports
+from .provider_response_cache import ProviderResponseCache
+
+
+
+class Provider(GObject.GObject, GtkSource.CompletionProvider):
+    """
+        This code is an LSP code completion plugin for Newton.
+        # NOTE: Some code pulled/referenced from here --> https://github.com/isamert/gedi
+    """
+    __gtype_name__ = 'LSPProvider'
+
+    def __init__(self):
+        super(Provider, self).__init__()
+
+        self.response_cache: ProviderResponseCache = None
+
+
+    def pre_populate(self, context):
+        ...
+
+    def do_get_name(self):
+        return "LSP Code Completion"
+
+    def do_match(self, context):
+        # Note: If provider is in interactive activation then need to check
+        # view focus as otherwise non focus views start trying to grab it.
+        # completion = context.get_property("completion")
+        # if not completion.get_view().has_focus(): return
+
+        iter = self.response_cache.get_iter_correctly(context)
+        iter.backward_char()
+        ch = iter.get_char()
+
+        # NOTE: Look to re-add or apply supporting logic to use spaces
+        # As is it slows down the editor in certain contexts...
+        # if not (ch in ('_', '.', ' ') or ch.isalnum()):
+        if not (ch in ('_', '.') or ch.isalnum()):
+            return False
+
+        buffer = iter.get_buffer()
+        if buffer.get_context_classes_at_iter(iter) != ['no-spell-check']:
+            return False
+
+        return True
+
+    def do_get_priority(self):
+        return 5
+
+    def do_activate_proposal(self, proposal, iter_):
+        buffer = iter_.get_buffer()
+        # Note: Flag mostly intended for SourceViewsMultiInsertState
+        #       to insure marker processes inserted text correctly.
+        buffer.is_processing_completion = True
+        return False
+
+    def do_get_activation(self):
+        """ The context for when a provider will show results """
+#        return GtkSource.CompletionActivation.NONE
+        return GtkSource.CompletionActivation.USER_REQUESTED
+#        return GtkSource.CompletionActivation.INTERACTIVE
+
+    def do_populate(self, context):
+        results   = self.response_cache.filter_with_context(context)
+        proposals = []
+
+        for entry in results:
+            proposals.append(
+                self.response_cache.create_completion_item(
+                    entry["label"],
+                    entry["text"],
+                    entry["info"]
+                )
+            )
+
+        context.add_proposals(self, proposals, True)