Duplicated signatures in transactions

[grarco]

Some of the transactions observed in mainnet are carrying duplicated inner signatures with the only difference in the two signature sections being the signer: in one of the two it is expressed as an address while in the other one as a public key. This behavior seems to happen on bundles containing a reveal_pk and a bond transaction.

When we construct the bundle we try to avoid duplicated SigningTxData structs to avoid this kind of situations but unfortunately it is still possible for two different instances of such type to lead to the same signature being produced. We should try to improve this check further or improve the logic that we use to discard duplicated sections