Add optional id property to test schema (#698)

[AnirudhJindal]

Description

This PR adds support for the optional id property to the test schema, enabling stable identifiers for test cases and individual tests as discussed in #698.

Changes

• Added optional id property to test case schema definition
• Added optional id property to individual test schema definition ($defs/test)
• Both id properties are optional (not in required array) for backward compatibility
• Added detailed descriptions explaining ID requirements:
  • Must be unique within the version
  • Should never change even if description changes
  • Enables stable tracking across file reorganization

Specification References

This change enables the behavior discussed in #698 where test cases can be tracked over time even when:

• Descriptions are clarified or modified
• Tests are moved within files
• Tests are recategorized between files

Schema Structure

Test Case Level

"id": {
  "description": "A stable, unique identifier for this test case. Must be unique within the version. Should never change even if the description or other properties change.",
  "type": "string"
}

Individual Test Level ($defs/test)

"id": {
  "description": "A stable, unique identifier for this test. Must be unique within the test case. Should never change even if the description or other properties change.",
  "type": "string"
}

Testing

• Validated JSON syntax with python -m json.tool
• Ran bin/jsonschema_suite check successfully
• Verified schema structure is correct
• Confirmed id is not in required arrays (optional for backward compatibility)
• Added descriptive commit message following repository guidelines

Design Rationale

• Optional now, required later: The property is initially optional to avoid breaking existing test files. Once all files have IDs, the property can be made required in a future PR.
• Minimal change: Only adds the id property definition, no other modifications to the schema structure.

Related Issue

Relates to #698

Next Steps

After this PR is merged:

1. Individual test files can be updated with UUID values (starting with enum.json)
2. A sanity check can be added to verify ID uniqueness
3. Once all files have IDs, the property can be made required

Review Notes

This is a foundational change that enables the work in #698. The actual addition of UUID values to test files will come in subsequent PRs (one file at a time per repository guidelines).

Looking forward to feedback! Happy to make any adjustments. :)