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/manifest.json

@@ -0,0 +1,7 @@
+{
+    "name": "Nanoesq Temp Buffer",
+    "author": "ITDominator",
+    "version": "0.0.1",
+    "support": "",
+    "requests": {}
+}