test(trade): use distinct signed payload for approve transaction

[Dark-Brain07]

What changed? Why?

Updated src/tests/trade_test.ts to use a distinct signed payload for the approve transaction in the broadcast test.

Why?
A TODO in the code noted that the test was using the same signed payload for both the main transaction and the approve transaction. By using a distinct payload, we verify that the broadcastTrade method correctly uses the specific approve_transaction_signed_payload and discriminates between the two.

Qualified Impact

This is a test-only change.

• Components affected: src/tests/trade_test.ts
• Impact of error: Incorrect test logic could lead to false positives/negatives in CI, but no production impact.
• Resolution: Fix the test file.

[cb-heimdall]

🟡 Heimdall Review Status

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