feat: Add support for package traits

[philprime]

Add project-spec support for enabling Swift package traits on remote and local package references. Traits are forwarded to XcodeProj so generated projects preserve the configured trait selections.

Configuration

packages:
  Sentry:
    path: ../..
    traits:
      - NoUIFramework

Remote packages support the same traits array. Omitted traits remain distinct from an explicit empty array, matching Xcode project serialization behavior.

Compatibility

Existing package declarations continue to generate without a traits key. The legacy localPackages syntax remains unchanged, and traits are intentionally configured only on top-level package references rather than target product dependencies.

This also updates XcodeProj from 9.10.1 to 9.14.0, the first release with Swift package trait support.

Testing

• swift test
• ProjectSpec and XcodeGenKit focused test suites

Closes #1585

[yonaskolb]

Looks good! Thank you @philprime

[philprime]

You are welcome @yonaskolb! I just noticed that I didn't add a CHANGELOG.md entry, do you want me to create a follow-up PR?

[yonaskolb]

You are welcome @yonaskolb! I just noticed that I didn't add a CHANGELOG.md entry, do you want me to create a follow-up PR?

No, that's fine. We used to require that, in the past, but it will get filled in on release

[philprime]

Thanks @yonaskolb 🙏 Do you have an estimate for when the next release of xcodegen will become available?