Add iOS unit tests for RNSentryIsPathUnderAllowedRoots

[antonis]

Follow-up from review of #6045.

The Android allowlist validator (RNSentryModuleImpl.isAllowedUri) ships in #6045 with 17 unit tests in RNSentryUriValidationTest. The equivalent iOS function — RNSentryIsPathUnderAllowedRoots in packages/core/ios/RNSentry.mm — has no unit tests in that PR.

The RNSentryCocoaTester workspace exists and is wired into native-tests.yml, so the infrastructure is already in place. What's needed:

1. Expose the file-scope static BOOL RNSentryIsPathUnderAllowedRoots(NSString *) to tests via a thin Obj-C class-method wrapper on RNSentry, declared in RNSentry+Test.h (matches the existing +captureReplayWithReturnValue pattern).
2. Add RNSentryCocoaTester/RNSentryCocoaTesterTests/RNSentryUriValidationTests.m covering:
   • empty path → NO
   • path containing .. component → NO
   • path under NSTemporaryDirectory() → YES
   • path under caches dir → YES
   • path under documents dir → YES
   • path under Library/ (e.g., Library/Cookies) → NO
   • absolute path outside sandbox (/etc/passwd) → NO
   • symlink inside tmp pointing outside the sandbox → NO (uses NSFileManager createSymbolicLinkAtURL in setUp/tearDown)
3. Wire the new file into RNSentryCocoaTester.xcodeproj (Xcode UI or xcodeproj ruby gem).

Mirrors the Android coverage so both platforms have parity.

[linear-code]

RN-595