Support Unified Trading Account, api v3

[yaroslavlsd]

Links:

• https://www.bitget.com/api-doc/spot/trade/Batch-Place-Orders
• https://github.com/ccxt/ccxt/pull/26272/files#diff-3d069846961a7023f8f5e3dd665bd0068763ae1bc669e22878693eedbcaf9a40

[yaroslavlsd]

By support response at 10/2025, only UTA v3 api can be used for UTA accounts, old classic account still can use old api v2