Fixes for quiescence back ported from lightning-kmp

[remyers]

This PR fixes some issues we found while porting quiescence to lightning-kmp.

We might find more changes, so this should stay in draft until we also have splicing with htlcs ported.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (61f1e1f) 85.85% compared to head (e2c1308) 85.85%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2779   +/-   ##
=======================================
  Coverage   85.85%   85.85%           
=======================================
  Files         216      216           
  Lines       18188    18196    +8     
  Branches      780      786    +6     
=======================================
+ Hits        15615    15622    +7     
- Misses       2573     2574    +1     

Files	Coverage Δ
...in/scala/fr/acinq/eclair/channel/fsm/Channel.scala	85.94% <100.00%> (+0.08%)	⬆️

... and 5 files with indirect coverage changes

[t-bast]

LGTM, I think we should integrate this PR. Github doesn't show me the action to restart the failed CI, maybe you'll need to rebase for that? There shouldn't be any conflict.