New for loops and some assert/require

[ajm188]

Description

This updates a small portion of the codebase, primarily to use the new range syntax, but then made some assert/require changes in files I happened to already be editing.

Related Issue(s)

#15193
#15182

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3a98b4c) 67.28% compared to head (d2703e3) 67.45%.
Report is 36 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15194      +/-   ##
==========================================
+ Coverage   67.28%   67.45%   +0.17%     
==========================================
  Files        1559     1560       +1     
  Lines      192056   193177    +1121     
==========================================
+ Hits       129219   130305    +1086     
- Misses      62837    62872      +35     

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[frouioui]

that's really cool

[ajm188]

note that coverage has decreased slightly because i also deleted some unused (and untested) code

[shlomi-noach]

Nice!