New OCT activity type for on-chain transactions

Adds OCT (On Chain Transactions) to the ActivityType enum for blockchain deposits and withdrawals. On-chain transaction activities now appear in activity feeds and events with this type.

• A new OCT value on the ActivityType enum.
• A new OCTActivityV2 schema (transfer_id and symbol) wired into ActivityV2DetailNTA for V2 activity events.

Broker API

Also adds the transfer_id field to the NonTradeActivity schema.

Affected Endpoints

• GET /v1/accounts/activities
• GET /v1/accounts/activities/{activity_type}
• GET /v2beta1/accounts/{account_id}/events/activities/{event_id}
• GET /v2beta1/events/activities

Trading API

• GET /v2/account/activities
• GET /v2/account/activities/{activity_type}
• GET /v2beta1/events/activities