Update [GULSwizzler ivarObjectForObjects] and add unit tests

[tejasd]

Updates [GULSwizzler ivarObjectForObjects] on

• Querying the class to fetch the ivars for. See fix(perf): avoid unsafe NSProxy delegate ivar lookup firebase/firebase-ios-sdk#16270
• Add logic to skip weak instance variables. See [Perf] Crash in objc_loadWeakRetained via -[PAGWeakProxy respondsToSelector:] — FPRProxyObjectHelper reads and ISA-swizzles a __weak delegate ivar firebase/firebase-ios-sdk#16469
• Adds unit tests

[tejasd]

/gemini review

[ncooke3]

How soon would this need to be released?

[paulb777]

Could there be an existing use case that depends on a weak ivar being swizzled?

[tejasd]

Could there be an existing use case that depends on a weak ivar being swizzled?

The existing usage decided whether to swizzle or not based on the protocol or the superclass of the instance variable - firebase/firebase-ios-sdk#16553.

This change (and the versioning constraints) would result in older versions of the SDK no longer swizzling weak instances - which IIUC would be an improvement (to prevent related crashes).

[tejasd]

How soon would this need to be released?

Ideally ASAP. Based on the versioning rules in https://github.com/firebase/firebase-ios-sdk (assuming this is a minor version bump) - users can benefit from it in https://github.com/firebase/firebase-ios-sdk/blob/main/FirebasePerformance/CHANGELOG.md#12140 (and potentially older).

firebase/firebase-ios-sdk#16553 also fixes it for future versions.