Remove temp cut buffer commands and cleanup related SourceView code

- Moved cut_to_temp_buffer and paste_temp_buffer commands to plugin
- Remove temp buffer state and timeout logic from SourceView
- Remove associated keybindings (Ctrl+K / Ctrl+U)
- Ignore "buffer" pseudo-path when filtering loaded files
- Ensure view receives focus after DnD file load

plugins/code/commands/nanoesq_temp_buffer/helpers.py

@@ -0,0 +1,24 @@
+# Python imports
+
+# Lib imports
+import gi
+
+from gi.repository import GLib
+
+# Application imports
+
+
+
+def clear_temp_cut_buffer_delayed(view: any):
+    if not hasattr(view, "_cut_temp_timeout_id"): return
+    if not view._cut_temp_timeout_id: return
+
+    GLib.source_remove(view._cut_temp_timeout_id)
+
+def set_temp_cut_buffer_delayed(view: any):
+    def clear_temp_buffer(view: any):
+        view._cut_buffer          = ""
+        view._cut_temp_timeout_id = None
+        return False
+
+    view._cut_temp_timeout_id = GLib.timeout_add(15000, clear_temp_buffer, view)