Expose requested PURL version in lookup results

[AgentGoose32]

Fixes #512

Summary

• Preserves the version from a package URL lookup request when the PURL includes one.
• Adds the requested version field to lookup JSON results only when a version was present in the purl parameter.
• Keeps versionless PURL lookup responses unchanged.
• Adds controller coverage for both versioned and versionless lookup responses.

Validation

• bundle install
• bundle exec ruby -c app/controllers/api/v1/packages_controller.rb
• bundle exec ruby -c test/controllers/api/v1/packages_controller_test.rb
• git diff --check

Note: targeted Rails controller test execution is blocked locally because PostgreSQL is not running on /tmp/.s.PGSQL.5432.