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

[tnull]

Based on #3336.

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

Followups: #3338.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.77%. Comparing base (053281f) to head (947cf72). Report is 1330 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3337      +/-   ##
==========================================
+ Coverage   89.66%   89.77%   +0.11%     
==========================================
  Files         126      126              
  Lines      103226   105591    +2365     
  Branches   103226   105591    +2365     
==========================================
+ Hits        92555    94796    +2241     
- Misses       7954     8089     +135     
+ Partials     2717     2706      -11     

Flag	Coverage Δ
	89.77% <ø> (+0.11%)	:arrow_up:

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[tnull]

Rebased on main after #3336 landed.

[tnull]

Closing in favor of doing fn-level rustfmt::skip first.