Cache schemas by explicit ID in AJV8Validator.isValid

[evshi]

Reasons for making this change

fixes #3692

For allOf/anyOf schemas, subschemas are compiled each time they are encountered if they lack an $id field. This can create poor performance for large lists or recursive refs. Leveraging the ajv cache to cache subschemas that have been encountered before greatly improves performance.

Checklist

• I'm updating documentation
  • I've checked the rendering of the Markdown text I've added
• I'm adding or updating code
  • I've added and/or updated tests. I've run npm run test:update to update snapshots, if needed.
  • I've updated docs if needed
  • I've updated the changelog with a description of the PR
• I'm adding a new feature
  • I've updated the playground with an example use of the feature

[evshi]

@heath-freenome updated, PTAL

[heath-freenome]

@evshi This looks pretty good! Can you update the CHANGELOG.md and add an 5.8.2 section for this change? And also rebase to main

[evshi]

@heath-freenome updated CHANGELOG and confirmed up to date with main