Don't lint $ref siblings for default/examples in Draft 7 and older

[staging-devin-ai-integration]

Skip default/examples $ref siblings in Draft 7 and older

Summary

This PR updates the ValidDefault and ValidExamples linter rules to respect JSON Schema draft semantics for $ref siblings:

• Draft 7 and older: if a schema object has $ref, the linter now skips linting default / examples siblings (they must be ignored by implementations).
• 2019-09 and 2020-12: existing behavior is preserved, so invalid default / examples siblings to $ref are still detected and removed.

It also adds regression tests for both rules covering:

• Draft-07 $ref sibling preservation
• Draft 2019-09 $ref sibling removal
• Draft 2020-12 $ref sibling removal

Review & Testing Checklist for Human

• Verify the dialect gating logic in ValidDefault::condition and ValidExamples::condition matches intended draft behavior (especially how vocabularies are populated).
• Confirm the new tests reflect the exact requirement: preserve in Draft-07, remove in 2019-09 and 2020-12 for invalid $ref siblings.
• Run an end-to-end lint/transform pass on representative schemas across drafts (Draft-07, 2019-09, 2020-12) to ensure there are no unexpected changes outside these two keywords.

Recommended test plan:

1. Run make configure compile
2. Run make
3. Manually inspect transformed output for schemas with { "$ref": ..., "default": ... } and { "$ref": ..., "examples": [...] } in Draft-07 vs 2019-09/2020-12

Notes

• Local verification run: make configure compile && make (passed)
• Link to Devin Session: https://staging.itsdev.in/sessions/110f86f5807c4d9fab1d2ca977a302ba
• Requested by: bot_apk

[staging-devin-ai-integration]

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