ci: upload coverage to Codecov

phpunit.xml already declares <source> + pcov is enabled in the
workflow. Emit Clover XML via --coverage-clover and upload it to
Codecov non-blockingly.

Requires CODECOV_TOKEN to be set as a repo secret.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: nficano

.github/workflows/test.yml

@@ -73,8 +73,18 @@ jobs:
         if: hashFiles('.php-cs-fixer.dist.php', '.php-cs-fixer.php') != ''
         run: vendor/bin/php-cs-fixer fix --dry-run --diff
 
-      - name: Run PHPUnit
-        run: vendor/bin/phpunit
+      - name: Run PHPUnit (with Clover coverage)
+        run: vendor/bin/phpunit --coverage-clover=coverage.xml
+
+      # Non-blocking: a Codecov outage cannot break CI.
+      - name: Upload coverage to Codecov
+        # codecov/codecov-action v6.0.1
+        uses: codecov/codecov-action@e79a6962e0d4c0c17b229090214935d2e33f8354 # v6.0.1
+        with:
+          fail_ci_if_error: false
+          flags: unittests
+          files: ./coverage.xml
+          token: ${{ secrets.CODECOV_TOKEN }}
 
       - name: Upload test artifacts on failure
         if: failure()