Resign next remote commit on reconnection

[t-bast]

We previously retransmitted our last commit_sig on reconnection if it hadn't been received by our peer, without changing it. This can be an issue for taproot channels when remote nodes don't use deterministic nonce derivation, because their nonce may be different on reconnection and our previous commit_sig would thus not be valid anymore.

We now re-sign the next commitment on reconnection, using the latest nonces we receive from channel_reestablish.

In the second commit, we remove the NextRemoteCommit case class, which is otherwise just a dumb wrapper around RemoteCommit.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 97.56098% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 88.91%. Comparing base (f93d02f) to head (ccf8d17).
⚠️ Report is 108 commits behind head on master.

Files with missing lines	Patch %	Lines
...in/scala/fr/acinq/eclair/channel/fsm/Channel.scala	90.90%	1 Missing ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3157      +/-   ##
==========================================
+ Coverage   86.43%   88.91%   +2.47%     
==========================================
  Files         242      218      -24     
  Lines       22607    20481    -2126     
  Branches      832      816      -16     
==========================================
- Hits        19541    18210    -1331     
+ Misses       3066     2271     -795     

Files with missing lines	Coverage Δ
...in/scala/fr/acinq/eclair/channel/Commitments.scala	95.92% <100.00%> (ø)
...c/main/scala/fr/acinq/eclair/channel/Helpers.scala	92.65% <100.00%> (+0.01%)	⬆️
...la/fr/acinq/eclair/channel/fsm/ErrorHandlers.scala	83.41% <100.00%> (ø)
...n/scala/fr/acinq/eclair/json/JsonSerializers.scala	96.00% <ø> (ø)
...ire/internal/channel/version5/ChannelCodecs5.scala	99.48% <100.00%> (-0.52%)	⬇️
...wire/internal/channel/version5/ChannelTypes5.scala	100.00% <100.00%> (ø)
...in/scala/fr/acinq/eclair/channel/fsm/Channel.scala	84.24% <90.90%> (-0.07%)	⬇️

... and 9 files with indirect coverage changes

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