[fix] accept infinity, inf and nan as real numbers

[biojppm]

re biojppm/rapidyaml#184

[codecov]

Codecov Report

Merging #60 (0dde083) into master (a34a59a) will increase coverage by 0.43%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #60      +/-   ##
==========================================
+ Coverage   92.51%   92.95%   +0.43%     
==========================================
  Files          50       50              
  Lines        9825    10002     +177     
==========================================
+ Hits         9090     9297     +207     
+ Misses        735      705      -30     

Impacted Files	Coverage Δ
src/c4/charconv.hpp	97.57% <100.00%> (+0.01%)	⬆️
src/c4/substr.hpp	98.83% <100.00%> (+0.02%)	⬆️
test/test_charconv.cpp	100.00% <100.00%> (ø)
test/test_substr.cpp	99.18% <100.00%> (+0.03%)	⬆️
src/c4/ext/fast_float_all.h	27.74% <0.00%> (+4.05%)	⬆️

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