CASTOR: Java 21 upgrade with dependency updates and test coverage improvements

[chiragkaushik-iqg]

Summary

This PR upgrades the CASTOR project to Java 21 and performs modernization across all modules.

Key Changes

• Upgraded project from legacy Java version to Java 21
• Updated libraries and dependency versions for compatibility
• Refactored code to resolve deprecated/removed API usage
• Fixed build issues across modules
• Ensured successful root-level build

Test Improvements

• Fixed existing failing unit tests
• Generated additional unit tests for low-coverage areas
• Improved module-level coverage to ≥ 80%
  • Example: Core module coverage ~87%

Modules Updated

• Parent
• Core
• Schema
• XML
• Codegen
• Diff
• xmlctf
• xmlctf-framework
• Xml-annotations
• anttask
• maven-plugins
• codegen-testcase-archetype

Validation

• All modules build successfully
• Project builds from root with tests
• Sonar analysis executed to validate coverage
• No functional changes intended (modernization only)

Notes

This upgrade was executed using a structured phase-wise approach with dependency analysis, roadmap planning, and controlled execution for each microservice.