Consolidate url-converter.test.mts: parameterize package type tests

Refactor repetitive package type conversion tests using it.each:
- Consolidate 17 toRepositoryUrl tests into 1 parameterized test
- Consolidate 11 toDownloadUrl tests into 1 parameterized test
- Consolidate 4 null-return validation tests into 1 parameterized test

Reduces ~250 lines while maintaining identical test coverage.

Author: jdalton