fix: dead code analysis inside for loops

[charles-cooper]

What I did

fixes #3223

(depends #3541)

How I did it

recurse into loop bodies when For nodes are encountered.

How to verify it

Commit message

unreachable code analysis did not analyze for loop bodies.
fix: in `find_terminating_node()`, recurse into the bodies of for loops.

Description for the changelog

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (af5c49f) 84.16% compared to head (9f99147) 84.20%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3731      +/-   ##
==========================================
+ Coverage   84.16%   84.20%   +0.03%     
==========================================
  Files          92       92              
  Lines       13133    13135       +2     
  Branches     2926     2927       +1     
==========================================
+ Hits        11054    11060       +6     
+ Misses       1659     1655       -4     
  Partials      420      420              

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