## Description
Closes https://github.com/stacks-sbtc/sbtc/issues/2133
## Changes
* Cache `NonceResponse`s in the Signer state machine and use these
responses to construct the nonce before returning signature shares.
* Cache `NonceResponse`s during DKG verification as well.
## Testing Information
I tested this on devenv and everything worked okay. I did see logs
saying "received a sweep NonceResponse without an active signing round".
I suppose this is kinda expected. If it's an issue in production, we can
revisit.
## Checklist
- [x] I have performed a self-review of my code
- [x] I have had an AI agent review my code