chore(database): deprecation warnings for v8 API ahead of future major release

[MichaelVerdon]

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	Aug 5, 2025 4:49pm

[mikehardy]

rebased to main to make sure it runs with current code after all the updates

squashed the commits to one and made the example app index have all the different test app lines (but with the others commented out)

runs 100% clean locally (which required lots of e2e namespace -> modular cleanup - amazing how many misses slipped in there!)

looks like it was kind of a bear to do, but looks good to me