feat(#117): add dotnet format check to CI pipeline (#154)

Insert `dotnet format --verify-no-changes --verbosity diagnostic` step
between `dotnet restore` and `dotnet build` so PRs that violate
.editorconfig formatting rules fail fast with clear diagnostic output.

Stacked on #152 which provides the nullable warning fixes needed
for the format check to pass.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: LeeCampbell

.github/workflows/ci.yml

@@ -22,6 +22,8 @@ jobs:
           cache-dependency-path: '**/*.csproj'
 
       - run: dotnet restore
+      - name: Check code formatting
+        run: dotnet format --verify-no-changes --verbosity diagnostic
       - run: dotnet build -c Release --no-restore /p:Version=${{ env.SEMVER }}
       - run: dotnet test ./HdrHistogram.UnitTests/HdrHistogram.UnitTests.csproj --no-build -c Release
       - run: dotnet pack ./HdrHistogram/HdrHistogram.csproj -c Release --no-build --include-symbols --no-restore /p:Version=${{ env.SEMVER }}