Support async `ChannelMonitorUpdate` persist for claims against closed channels

[TheBlueMatt]

Based on #3413, this finally implements async ChannelMonitorUpdate persistence against closed channels. After all the prep, its...not all that bad. Would still like to write an additional test for the last second-to-commit though the changes in that commit do show it has some coverage.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 90.05102% with 39 lines in your changes missing coverage. Please review.

Project coverage is 89.60%. Comparing base (8da30df) to head (8fca379).

Files with missing lines	Patch %	Lines
lightning/src/ln/channelmanager.rs	86.36%	21 Missing and 15 partials :warning:
lightning/src/ln/chanmon_update_fail_tests.rs	98.13%	1 Missing and 1 partial :warning:
lightning/src/chain/channelmonitor.rs	80.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3414 +/- ## ========================================== - Coverage 89.60% 89.60% -0.01% ========================================== Files 129 129 Lines 105506 105646 +140 Branches 105506 105646 +140 ========================================== + Hits 94540 94664 +124 - Misses 8212 8220 +8 - Partials 2754 2762 +8 ```

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