rustfmt: Run on some smaller files in lightning/ln

[tnull]

We run the formatter on some smallish files.

[ldk-reviews-bot]

👋 Thanks for assigning @TheBlueMatt 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.

[vincenzopalazzo]

LGTM

[martinsaposnic]

LGTM. I wasn’t aware of rustfmt_excluded_files, I'm curious why it's needed

[TheBlueMatt]

one nit

[TheBlueMatt]

I wasn’t aware of rustfmt_excluded_files, I'm curious why it's needed

Because, sadly, rustfmt on some of our files creates some really unreadable results. So we're doing it iteratively, applying it to more and more files over time and removing things from the excluded list.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.50%. Comparing base (46cb5ff) to head (8df643d).
Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3724      +/-   ##
==========================================
+ Coverage   89.11%   89.50%   +0.39%     
==========================================
  Files         156      156              
  Lines      123435   125924    +2489     
  Branches   123435   125924    +2489     
==========================================
+ Hits       109995   112713    +2718     
+ Misses      10758    10541     -217     
+ Partials     2682     2670      -12     

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[tnull]

Going ahead landing this with one ACK as it's trivial and the nit was addressed.