Add date field normalization and custom field value warnings

What’s New

The Partner API now handles date custom fields more intelligently:

Date Format Normalization

• Automatically normalizes date custom field values to ISO 8601 format (YYYY-MM-DD)
• Returns warnings in the API response when dates are normalized from non-ISO formats
• Helps prevent data inconsistencies from varied date input formats

Improved Custom Fields Response

• Custom fields now include a nested customFields object in person responses alongside the existing flat camelCase format
• Custom field input now accepts both formats: flat camelCase and nested object
• Maximum flexibility for integrators building on the Partner API

These improvements make the Partner API more robust and developer-friendly when working with custom field values.