data: provide frequency and modem preset for meshcore (#694)

* data: provide frequency and modem preset for meshcore

* data: provide frequency and modem preset for meshcore

* ingestor: address review comments

* fix: remove duplicate _mark_packet_seen entry from handlers __all__

* ci: install meshcore in Python workflow

protocols/meshcore.py now imports meshcore at module level (required to
fix a self-referential import failure after the providers/ → protocols/
rename).  test_provider_unit.py imports that module unconditionally, so
meshcore must be present in the test environment.

* data: run black

.github/workflows/python.yml

@@ -39,7 +39,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install black pytest pytest-cov meshtastic
+        pip install black pytest pytest-cov meshtastic meshcore
     - name: Test with pytest and coverage
       run: |
         mkdir -p reports