Get block trade
Retrieve a specific block trade by ID with full details.
Returns complete block trade information including status, trade details,
signatures, and offers.
**Access:** Available to initiator, required signers,
or accounts with submitted offers.
**Returns:**
- Block ID and status
(CREATED, OFFER_COLLECTION, READY_TO_EXECUTE, EXECUTING, COMPLETED, CANCELLED)
- Market-specific trade details with orders and fill information
- All collected signatures from required signers
- Creation time, last update, expiration, and participant information