rustfmt: Run on the routing directory (3/3)

[tnull]

Based on #3337.

This is PR 3/3, formatting the rest of routing.

[codecov]

Codecov Report

Attention: Patch coverage is 95.94203% with 42 lines in your changes missing coverage. Please review.

Project coverage is 89.85%. Comparing base (a0d0f02) to head (8a8e6fa).

Files with missing lines	Patch %	Lines
lightning/src/routing/utxo.rs	92.12%	34 Missing and 5 partials ⚠️
lightning/src/routing/test_utils.rs	99.44%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3338      +/-   ##
==========================================
+ Coverage   89.60%   89.85%   +0.24%     
==========================================
  Files         126      126              
  Lines      102750   106502    +3752     
  Branches   102750   106502    +3752     
==========================================
+ Hits        92069    95695    +3626     
- Misses       7948     8115     +167     
+ Partials     2733     2692      -41     

Flag	Coverage Δ
	89.85% <95.94%> (+0.24%)	⬆️

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