fix: add explicit platform versions to Package.swift

[ncooke3]

nanopb fix for firebase/firebase-ios-sdk#16244

The Package.swift did not provide an explicit platforms: [SupportedPlatform]?. On Xcode 27 beta, this caused watchOS builds to fail. Only watchOS seems to be affected by not being specified in the platforms array.:

/Users/nickcooke/Library/Developer/Xcode/DerivedData/app-check-bazhoueefjmiowavinzydkvkoqvm/SourcePackages/checkouts/promises/Package.swift: error: The watchOS Simulator deployment target 'WATCHOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 27.0.x. (in target 'Promises' from project 'Promises' at path '/Users/nickcooke/Library/Developer/Xcode/DerivedData/app-check-bazhoueefjmiowavinzydkvkoqvm/SourcePackages/checkouts/promises/Package.swift')

Perhaps we should be setting watchOS(.v9) as we are explicitly specifying a version out of the logged range, but this would violate Firebase's currently watchOS min. supported version.

Observations:

• watchOS is the only platform complaining about the missing specifier
• adding the non-watchOS platforms is not necessary for those respective platforms to build
  • to future proof, I'm adding an explicit platforms array with all supported versions
    • this package's swift tools version does not support visionOS or macCatalyst specifiers
      • building visionOS 27 does however pass
      • building macCatalyst 26.5 with Xcode 27 passes (do not have beta macOS installed so can't test macCatalyst 27)

Mirroring the platform support versions from the promises podspec:
From

promises/PromisesSwift.podspec

Lines 19 to 23 in d6d659a

	s.ios.deployment_target = '9.0'
	s.osx.deployment_target = '10.11'
	s.tvos.deployment_target = '9.0'
	s.watchos.deployment_target = '2.0'
	s.visionos.deployment_target = '1.0'

  s.ios.deployment_target  = '9.0'
  s.osx.deployment_target  = '10.11'
  s.tvos.deployment_target = '9.0'
  s.watchos.deployment_target = '2.0'
  s.visionos.deployment_target = '1.0'

Versioning

We should tag this version as a patch release: 2.4**.1**, so existing Firebase versions pick this up.

https://github.com/firebase/firebase-ios-sdk/blob/7f9f7d761627c827a0c6d7a410c9a111bf220f18/Package.swift#L136-L139

   .package(
      url: "https://github.com/google/promises.git",
      "2.4.0" ..< "3.0.0"
    ),

[ncooke3]

Tests look like unrelated flakes.