Support normal channel operation with async signing

[waterson]

This is a do-over of #2653, wherein we support asynchronous signing for 'normal' channel operation. This involves allowing the following ChannelSigner methods to return an Err result, indicating that the requested value is not available:

• get_per_commitment_point
• release_commitment_secret
• sign_counterparty_commitment

When the value does become available, channel operation can be resumed by invoking signer_unblocked.

Note that this adds the current and next per-commitment point to the state that is persisted by the channel monitor.

[coderabbitai[bot]]

Walkthrough

The recent updates across various files in a Rust-based codebase focus on enhancing asynchronous operations, particularly around signing processes. These changes include the addition of new constants, modifications to the SignerProvider, and updates to message handling and error management. There's also a notable shift in how per_commitment_points are handled, alongside improved logging for debugging and more robust test utilities.

Changes

Files	Summary
fuzz/src/chanmon_consistency.rs, lightning/src/ln/channelmanager.rs, lightning/src/util/test_channel_signer.rs	Introduced new asynchronous operation constants, updated SignerProvider, added debugging logs, and refined message handling logic.
lightning/src/chain/channelmonitor.rs, lightning/src/chain/onchaintx.rs	Altered how per_commitment_point is assigned and used, affecting on-chain transaction handling.
lightning/src/ln/functional_test_utils.rs, lightning/src/ln/functional_tests.rs	Enhanced test utilities with new functions, improved error handling, and explicit result unwrapping.
lightning/src/sign/mod.rs	Modified ChannelSigner trait to include error handling by returning Result types.

🐇✨ In the realms of code, where the lightning arcs, A rabbit hopped through, leaving whimsical marks. With each line refined, and errors unwound, A trail of cleaner code is what it found. 🌟🌱

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 65.59865% with 204 lines in your changes missing coverage. Please review.

Project coverage is 88.99%. Comparing base (51d9ee3) to head (8db91d7). Report is 1848 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/channel.rs	71.56%	105 Missing and 15 partials :warning:
lightning/src/util/test_channel_signer.rs	36.25%	51 Missing :warning:
lightning/src/ln/functional_test_utils.rs	0.00%	12 Missing and 6 partials :warning:
lightning/src/ln/channelmanager.rs	73.68%	12 Missing and 3 partials :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2849      +/-   ##
==========================================
- Coverage   89.18%   88.99%   -0.20%     
==========================================
  Files         116      116              
  Lines       93098    93477     +379     
  Branches    93098    93477     +379     
==========================================
+ Hits        83034    83189     +155     
- Misses       7538     7733     +195     
- Partials     2526     2555      +29     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[TheBlueMatt]

One more thing we need to add to docs here before we ship is note that the signing validate_* methods may be called for two different commitments at the same height in rare cases. Specifically, if we receive a commitment update, pass it to the signer, then shut down without persisting anything we may restart, reconnect, and get a different commitment update from our peer. So the signer needs to handle this (we shouldn't need to deal with it in the actual sign methods because we wait for the monitor to persist before calling those).

[TheBlueMatt]

Supersceded by #3115, #3150, #3152, etc.