Remove extra loop var copies

[sevein]

In preparation for the go1.22 release, this pull request removes the copy of the loop variable that we used to need to prevent sharing in per-iteration closures or goroutines. I haven't found yet a tool that can remove these automatically, for now I find them in vscode using \b(\w+)\s*:=\s*\1\b$. Or:

grep --recursive --include=\*.go --perl-regexp '\b(\w+)\s*:=\s*\1\b$' .

I'll keep this as a draft until go1.22 is released.

Context: https://go.dev/wiki/LoopvarExperiment.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3c851dd) 45.30% compared to head (2ff601c) 45.29%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #852      +/-   ##
==========================================
- Coverage   45.30%   45.29%   -0.02%     
==========================================
  Files          93       93              
  Lines        5039     5036       -3     
==========================================
- Hits         2283     2281       -2     
+ Misses       2553     2552       -1     
  Partials      203      203              

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