chore(auth): deprecations for v8 API ahead of future major release

[russellwheatley]

Description

Related issues

Release Summary

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
  • Yes
• My change supports the following platforms;
  • Android
  • iOS
  • Other (macOS, web)
• My change includes tests;
  • e2e tests added or updated in packages/\*\*/e2e
  • jest tests added or updated in packages/\*\*/__tests__
• I have updated TypeScript types that are affected by my change.
• This is a breaking change;
  • Yes
  • No

Test Plan

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Name	Status	Preview	Comments	Updated (UTC)
react-native-firebase	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jul 1, 2025 1:12pm

[russellwheatley]

Need to fix this e2e test: https://github.com/invertase/react-native-firebase/actions/runs/15903535182/job/44852226924?pr=8590#step:18:1110

Not sure why, but seems android/iOS e2e tests don't actually report what failed. Found this test didn't work via "Other" CI run.

[mikehardy]

One of the big ones - nice - LGTM - rebased to main / squashed - waiting for CI