Math: make sign() branchless and constexpr

[sthalik]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.69%. Comparing base (69d02ad) to head (4ed3ad5).
⚠️ Report is 623 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #651      +/-   ##
==========================================
+ Coverage   82.41%   83.69%   +1.27%     
==========================================
  Files         564      563       -1     
  Lines       44332    41042    -3290     
==========================================
- Hits        36538    34349    -2189     
+ Misses       7794     6693    -1101     

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