Replace utils/jay_diff.py with jaydiff package from jayfield/jaypy

Remove the local copy of jay_diff and its tests/data; switch all four
import sites to `jaydiff.diff.diff_full` / `jaydiff.merge.merge_full`
from the shared Gitea package (http://192.168.22.90:3001/jayfield/jaypy).
Add the package as a VCS dependency in requirements.txt.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

requirements.txt

@@ -1,5 +1,6 @@
 carconnectivity
 carconnectivity-connector-volkswagen
+jaydiff @ git+http://192.168.22.90:3001/jayfield/jaypy.git
 PyQt5
 pyqtgraph
 pytest