Mithril relay broadcasts signer registrations in P2P

[jpraynaud]

Content

This PR includes the implementation of a prototypical decentralized signer registration with the P2P network of the Mithril relay:

• signer registration messages are broadcast to the P2P network
• signer registration messages are repeated at regular interval in order to support:
  • lost messages on the P2P network (e.g. due to network connectivity between peers)
  • newly signer/aggregator joining the network (to avoid 1 more epoch delay before being able to contribute)
  • recently offline signer/aggregator (to avoid 1 more epoch delay before being able to contribute)

Pre-submit checklist

• Branch
  • [x] Tests are provided (if possible)
  • [ ] Crates versions are updated (if relevant)
  • [x] Commit sequence broadly makes sense
  • [x] Key commits have useful messages
• PR
  • [x] No clippy warnings in the CI
  • [x] Self-reviewed the diff
  • [x] Useful pull request description
  • [ ] Reviewer requested

Issue(s)

Closes #1587

[github-actions[bot]]

Test Results

    3 files  ±0     43 suites  +1   8m 5s :stopwatch: -20s   924 tests +4    924 :white_check_mark: +4  0 :zzz: ±0  0 :x: ±0  1 018 runs  +4  1 018 :white_check_mark: +4  0 :zzz: ±0  0 :x: ±0 

Results for commit 07c14d8f. ± Comparison against base commit 2d3b4630.

This pull request removes 1 and adds 5 tests. Note that renamed tests count towards both.

mithril-relay::tests ‑ should_receive_signatures_from_signers_when_subscribed_to_pubsub

mithril-relay ‑ repeater::tests::should_do_nothing_when_message_not_exists
mithril-relay ‑ repeater::tests::should_do_nothing_when_message_not_exists_with_expected_delay
mithril-relay ‑ repeater::tests::should_repeat_message_when_exists
mithril-relay ‑ repeater::tests::should_repeat_message_when_exists_with_expected_delay
mithril-relay::register_signer_signature ‑ should_receive_registrations_from_signers_when_subscribed_to_pubsub

:recycle: This comment has been updated with latest results.