Rustfmt parts of channelmanager.rs

[joostjager]

Prepare for #3957

[ldk-reviews-bot]

I've assigned @tankyleo as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

[codecov]

Codecov Report

❌ Patch coverage is 79.41176% with 28 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.93%. Comparing base (55baa15) to head (0d56fb7).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/channelmanager.rs	79.41%	27 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3960      +/-   ##
==========================================
- Coverage   88.94%   88.93%   -0.02%     
==========================================
  Files         173      173              
  Lines      123794   123876      +82     
  Branches   123794   123876      +82     
==========================================
+ Hits       110114   110165      +51     
- Misses      11227    11255      +28     
- Partials     2453     2456       +3     

Flag	Coverage Δ
fuzzing	22.17% <0.00%> (-0.04%)	⬇️
tests	88.75% <79.41%> (-0.02%)	⬇️

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[tankyleo]

Reproduced both commits on my machine.

[ldk-reviews-bot]

👋 The first review has been submitted!

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