Registration and signing flow follow-ups

[HCastano]

Over the series of PRs I've opened related to registration and signing there have been a
few follow ups noted. I don't think its necessarily worthwhile to open an issue for each
one, so I'm just gonna dump them here.

If anything does end up requiring more in depth discussions then an individual issue can
be opened.

• Implement the message passing as described in the Tofino spec
• Do we need to check who when jumpstarting network?
• Add documentation for new flows
• Do we need hardcoded keyshares in the testing environment?
• Look into why we use BoundedVec vs. OtherBoundedVec
• Add CLI support for batch registrations?
• Better coupling for test setup function
• Improve get_sign_tx_data flow in tests