fix: handle serializedTxHex format in TSS verifyTransaction

[bhuvanr159]

TICKET: CHALO-380

Summary

• Issue: TRX MPC wallet withdrawals were failing with UtilsError: Number of contracts is greater than 1.

• Root cause: verifyTransaction is called twice during the TSS signing flow:

  1. From prebuildAndSignTransaction (wallet.ts:2480) — txHex is serializedTxHex, a full JSON string ({"txID":"...","raw_data":{...},"raw_data_hex":"..."})
  2. From ECDSA signing flow (ecdsa.ts:761) — txHex is signableHex, raw protobuf hex bytes

  The TSS branch only handled case 2 (protobuf hex). When case 1 passed a JSON string, the protobuf decoder produced garbage data and threw the error.

• Fix: Detect the format by attempting JSON.parse(txHex) — if it succeeds, extract raw_data_hex from the parsed JSON; if it fails, treat txHex as raw protobuf hex. This mirrors the pattern used by the builder's own getTxReceipt() method in wrappedBuilder.ts.

Test plan

• Added unit tests for serializedTxHex (JSON string) path — validates success and amount-mismatch failure
• Existing unit tests for signableHex (protobuf) path still pass
• All 115 TRX unit tests pass (nx run @bitgo/sdk-coin-trx:unit-test)
• TypeScript compilation clean (tsc --noEmit)
• Manual test: TRX MPC wallet withdrawal on testnet