Travel Rule schema refinements on crypto funding endpoints

Refines how Travel Rule schemas are described in the Broker and Trading API specs. Accepted and returned values are unchanged.

• The TravelRuleRequiredField schema now expresses its field options as an OpenAPI 3.1 array-or-null schema instead of the legacy nullable flag.
• Removes duplicate Travel Rule validation error examples from the TravelRuleValidationError schema; the same examples remain available through the shared components.

Broker API

• POST /v1/accounts/{account_id}/wallets/transfers
• POST /v1/accounts/{account_id}/wallets/whitelists
• PATCH /v1/accounts/{account_id}/wallets/whitelists/{whitelisted_address_id}/travel-rule-info

Trading API

• POST /v2/wallets/transfers
• POST /v2/wallets/whitelists
• PATCH /v2/wallets/whitelists/{whitelisted_address_id}/travel-rule-info