implement basic github action comment reporting target diffs (#9022)

This is missing logic:
- report average
- don't bother reporting if the results are negligeable
- praise the user if it's improving the situation
- shame the user if it's not improving the situation

.github/workflows/main_matrix.yml

@@ -233,6 +233,40 @@ jobs:
           description: "Download firmware-${{matrix.arch}}-${{ needs.version.outputs.long }}.zip. This artifact will be available for 90 days from creation"
           github-token: ${{ secrets.GITHUB_TOKEN }}
 
+  shame:
+    if: github.repository == 'meshtastic/firmware'
+    continue-on-error: true
+    runs-on: ubuntu-latest
+    needs: [build]
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          filter: blob:none # means we download all the git history but none of the commit (except ones with checkout like the head)
+          fetch-depth: 0
+      - name: Download the current manifests
+        uses: actions/download-artifact@v7
+        with:
+          path: ./manifests-new/
+          pattern: manifest-*
+          merge-multiple: true
+      - name: Upload combined manifests for later commit and global stats crunching.
+        uses: actions/upload-artifact@v6
+        id: upload-manifest
+        with:
+          name: manifests-all
+          overwrite: true
+          path: |
+            manifests-new/*.mt.json
+      - name: Find the merge base
+        run: echo "MERGE_BASE=$(git merge-base "origin/$base" "$head")" >> $GITHUB_ENV
+        env:
+          base: ${{ github.base_ref }}
+          head: ${{ github.head_ref }}
+      - name: Download the old manifests
+        run: gh run download -R ${{ github.repository }} --commit ${{ env.MERGE_BASE }} --name manifests-all --dir manifest-old/
+      - name: Do scan and post comment
+        run: python3 bin/shame.py ${{ github.event.pull_request.number }} manifests-old/ manifests-new/
+
   release-artifacts:
     runs-on: ubuntu-latest
     if: ${{ github.event_name == 'workflow_dispatch' && github.repository == 'meshtastic/firmware' }}