Track attempts to sign with off-curve keys

[t-nelson]

Problem

Moving derived addresses off the ed25519 curve discards mathematical guarantees for what their capabilities are within the cryptosystem. We do the known checks to prevent these values being used to verify signatures. Observing someone doing so may indicate an attempted unknown attack. We should keep track of these events.

Proposed Solution

Get the appropriate error types surfaced from ed25519-dalek
Add logging, metrics and alerts