fix(validator): handle built-in custom formats correctly

[heitorlessa]

Issue #, if available: #496

Description of changes:

JSONSchema Draft 7 has support for custom built-in formats like date-time. This PR fixes a malformed input to the upstream JSON validator (fastjsonschema) which cannot differentiate between custom format and custom built-in formats.

If no custom formats are explicitly passed we default to a Dict when passing that as input to fastjsonschema. This leads to the right fallback mechanism in the upstream validator to search for built-in custom formats.

Example JSON schema field that triggered it:

"message": { "$id": "#/properties/message", "type": "string", "format": "date-time", "title": "The message", "examples": ["hello world"], },

Checklist

• Meet tenets criteria
• Update tests
• Update docs
• PR title follows conventional commit semantics

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