LSPS2ServiceHandler API: Avoid explictly dropping locks

[tnull]

Follow-up to #4059.

We previously added some explict drops to make sure to drop locks before persisting. While clippy warned us about them, they seemed perfectly functional. However, it weirdly seems that cargo will run the same static analysis on dependencies, which has LDK Node builds fail with many dreaded 'isn't Send' error whenever we touch the async LSPS2ServiceHandler API.

Here, we simply believe clippy that this is a bad idea and use scoping over explict drops to ensure we don't hold them anymore when persisting.

Best reviewed with git diff --ignore-all-space, which makes the diff trivial.

[ldk-reviews-bot]

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[codecov]

Codecov Report

❌ Patch coverage is 81.69014% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.53%. Comparing base (7926fb9) to head (acb584d).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning-liquidity/src/lsps2/service.rs	81.69%	11 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4124      +/-   ##
==========================================
- Coverage   88.54%   88.53%   -0.01%     
==========================================
  Files         179      179              
  Lines      134333   134329       -4     
  Branches   134333   134329       -4     
==========================================
- Hits       118939   118928      -11     
- Misses      12634    12646      +12     
+ Partials     2760     2755       -5     

Flag	Coverage Δ
fuzzing	21.79% <ø> (ø)
tests	88.37% <81.69%> (-0.01%)	⬇️

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[joostjager]

Diff looks completely equivalent. Somewhat unsatisfying to not fully understand the root cause.

[ldk-reviews-bot]

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