Implement Codecov coverage badge with Tycho-compatible configuration

- Configure jacoco-maven-plugin in org.moreunit.build/pom.xml with a coverage profile.
- Use @{argLine} in tycho-surefire-plugin for Jacoco agent injection.
- Initialize <argLine> property in parent POM to prevent literal '@{argLine}' errors in standard builds.
- Create .github/workflows/coverage.yml for automated coverage reporting.
- Add Codecov badge to README.md.

Co-authored-by: RoiSoleil <3462260+RoiSoleil@users.noreply.github.com>

Author: google-labs-jules[bot]

org.moreunit.build/pom.xml

@@ -34,6 +34,7 @@
     <tests.use.ui>false</tests.use.ui>
 
     <target.platform.classifier>eclipse-latest</target.platform.classifier>
+    <argLine></argLine>
 
   </properties>
   <build>