fix: Rounding behaviour for f32 values with "HalfAwayFromZero" mode

[alexander-beedie]

The f32 path with "RoundMode::HalfAwayFromZero" was using round_ties_even instead of round. Fixed, and added explicit test coverage for f16/f32/f64 values that triggers the tiebreaks that found the bug 👍

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.39%. Comparing base (375fdc8) to head (f5482a2).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #26624      +/-   ##
==========================================
+ Coverage   81.38%   81.39%   +0.01%     
==========================================
  Files        1794     1794              
  Lines      245003   245002       -1     
  Branches     3080     3080              
==========================================
+ Hits       199393   199428      +35     
+ Misses      44824    44788      -36     
  Partials      786      786              

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