feat: working agent broadcast

[jrriehl]

This is what's needed to make the broadcast work from the agent.

[AbbasAliLokhandwala]

@jrriehl the code fails if amount entered in decimal format eg 1.3
Also the amount entered is taken in aTestFet instead of FET (probably the reason for above error too)
Agent should convert the amount before creating txn payload for signature

[jrriehl]

Yes, good catch. I needed to multiply by 10**18 since we were sending FET amounts to the wallet previously, but now since the txs are serialized, we need to send afet / atestfet/. Anyway, this is fixed now.