Function verifyTempoTransaction

Verify an mppx-native Tempo Transaction credential off-chain.

Checks:

1. The serialized payload is a Tempo Transaction (0x76 or 0x78 prefix)
2. The transaction is signed by the sender (has signature and from)
3. The batch calls include a transfer to expectedRecipient with amount >= expectedValue using the correct token contract

Does NOT verify the cryptographic signature against the chain — full signature verification requires eth_call on the Tempo chain (see mppx server implementation). OMPX's off-chain check validates structure only; the on-chain broadcast will reject invalid signatures.