New "isin" and "cusip" fields on the Global Asset schema

Broker API

Adds isin and cusip fields to the GlobalAsset schema, exposed independently. Both are optional and returned based on licensing.

• Deprecates external_id and external_id_type, which will be removed on 2026-12-18. Use isin or cusip instead.

Affected Endpoints

• GET /v2beta1/assets
• GET /v2beta1/assets/{symbol_or_asset_id}