ci: add NuGet publish workflow

.github/workflows/publish.yml

@@ -0,0 +1,62 @@
+name: Publish NuGet Package
+
+on:
+  release:
+    types:
+      - published
+
+permissions:
+  contents: read
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Setup .NET SDK
+        uses: actions/setup-dotnet@v4
+        with:
+          global-json-file: global.json
+
+      - name: Resolve package version
+        id: version
+        shell: bash
+        run: |
+          version="${GITHUB_REF_NAME#v}"
+          if [[ "$version" =~ ^[0-9]+\.[0-9]+$ ]]; then
+            version="$version.0"
+          fi
+          if [[ ! "$version" =~ ^[0-9]+\.[0-9]+\.[0-9]+([-+][0-9A-Za-z.-]+)?$ ]]; then
+            echo "Release tag '$GITHUB_REF_NAME' does not resolve to a SemVer package version." >&2
+            exit 1
+          fi
+          echo "package-version=$version" >> "$GITHUB_OUTPUT"
+
+      - name: Restore dependencies
+        run: dotnet restore
+
+      - name: Build
+        run: dotnet build -c Release --no-restore
+
+      - name: Run tests
+        run: dotnet test -c Release --no-build --logger "trx;LogFileName=test-results.trx" --results-directory TestResults
+
+      - name: Pack
+        run: >
+          dotnet pack src/FixedPointNano/FixedPointNano.csproj
+          -c Release
+          --no-build
+          -o artifacts
+          /p:PackageVersion=${{ steps.version.outputs.package-version }}
+
+      - name: Publish package
+        env:
+          NUGET_API_KEY: ${{ secrets.NUGET_API_KEY }}
+        run: >
+          dotnet nuget push artifacts/*.nupkg
+          --api-key "$NUGET_API_KEY"
+          --source "https://api.nuget.org/v3/index.json"
+          --skip-duplicate