feat(sdk-coin-sui): handle fab balance instruction

[abhishekagrawal080]

TICKET: CSHLD-948

BitGoJS/modules/sdk-coin-sui/src/lib/transferBuilder.ts

1. Fixed _fundsInAddressBalance JSDoc — removed incorrect claim that Sui automatically combines address balance into the gas coin when payment is non-empty
2. Updated buildSuiTransaction() JSDoc from "three paths" to "four paths", adding Path 2c description
3. Added Path 2c logic: when self-pay AND gasData.payment.length > 0 AND fundsInAddressBalance > 0, explicitly calls redeem_funds(withdrawal(addrBal)) + MergeCoins(gas, [addrCoin]) before SplitCoins

BitGoJS/modules/sdk-coin-sui/test/unit/transactionBuilder/transferBuilder.ts
4. Updated the existing Path 2c test to assert the correct PTB structure: MoveCall → MergeCoins → SplitCoins → TransferObjects (was incorrectly asserting SplitCoins at command 0)

[linear-code]

CSHLD-948