New "partial_fill" execution type on trade activity events

partial_fill has been added to the execution_type enum on the ActivityV2DetailTRD schema. Activity event streams already emit partial_fill for partially filled trades; the API description now documents it alongside fill, trade_correct, and trade_bust. Existing enum values are unchanged.

Broker API

• GET /v2beta1/events/activities
• GET /v2beta1/accounts/{account_id}/events/activities/{event_id}

Trading API

• GET /v2beta1/events/activities