rustfmt: Run on the routing directory (2/3)

[tnull]

Based on #3336.

This is PR 2/3, just formatting router.rs.

Followups: #3338.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.80%. Comparing base (a0d0f02) to head (01e58df).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3337      +/-   ##
==========================================
+ Coverage   89.60%   89.80%   +0.20%     
==========================================
  Files         126      126              
  Lines      102750   105591    +2841     
  Branches   102750   105591    +2841     
==========================================
+ Hits        92069    94830    +2761     
- Misses       7948     8064     +116     
+ Partials     2733     2697      -36     

Flag	Coverage Δ
	89.80% <ø> (+0.20%)	⬆️

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