test(yaml): test float handling

[kt3k]

part of #3764

This improves the test coverage of std/yaml. Added test cases which exercise the handling of floats.

[codecov-commenter]

Codecov Report

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

Project coverage is 92.26%. Comparing base (860cf0e) to head (ce47eac).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4850      +/-   ##
==========================================
+ Coverage   92.04%   92.26%   +0.22%     
==========================================
  Files         487      487              
  Lines       41535    41535              
  Branches     5365     5394      +29     
==========================================
+ Hits        38230    38322      +92     
+ Misses       3247     3156      -91     
+ Partials       58       57       -1     

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