feat(castor): remove antlr library and use regex instead

[goncalo-frade-iohk]

Overview

Removes Antler dependency and uses regex for parsing DID and DIDUrl

Checklist

My PR contains...

• [ ] No code changes (changes to documentation, CI, metadata, etc.)
• [ ] Bug fixes (non-breaking change which fixes an issue)
• [x] Improvements (misc. changes to existing features)
• [ ] Features (non-breaking change which adds functionality)

My changes...

• [ ] are breaking changes
• [x] are not breaking changes
• [ ] If yes to the above: I have updated the documentation accordingly

Documentation

• [x] My changes do not require a change to the project documentation
• [ ] My changes require a change to the project documentation
• [ ] If yes to the above: I have updated the documentation accordingly

Tests

• [ ] My changes can not or do not need to be tested
• [x] My changes can and should be tested by unit and/or integration tests
• [x] If yes to the above: I have added tests to cover my changes
• [x] If yes to the above: I have taken care to cover edge cases in my tests