JSON emitting: improve handling of nan, inf and some floats

[biojppm]

For example, the tree

{
  inf: [inf, .inf, .Inf, .INF, -inf, -.inf, -.Inf, -.INF],
  nan: [nan, .nan, .NaN, .NAN],
  dot: [.1, 1., .2e2, 10., -.2, -2.],
  zero: [10, 01],
  normal: [0.1, 0.2e3, 4.e5],
}

is now emitted to JSON as:

{
  "inf": [".inf",".inf",".inf",".inf","-.inf","-.inf","-.inf","-.inf"],
  "nan": [".nan",".nan",".nan",".nan"],
  "dot": [0.1,1.0,0.2e2,10.0,-0.2,-2.0],
  "zero": [10,"01"],
  "normal": [0.1,0.2e3,4.e5]
}

Previously, some inf and nan cases were emitted without quotes. Note also the added zeroes for some floats, eg .1 or -2., which turn into 0.1 and -2.0 in JSON.

I tried using "8e888" for inf as suggested in #312 but this value cannot be parsed by to_chars() (see proof in added tests), which prevents roundtrip equivalence. So I opted for a sensible ".inf" string for all inf cases.

Fixes #312
Fixes #535

[biojppm]

@davidrudlstorfer @captain-yoshi @sebproell Tagging you here because of #535 and #312 .

Please take a look at this PR; IMO it addresses the problems discussed in those issues.

As I said above (and you can verify in the tests added in this PR), 8e888 cannot be used to signify infinity because fast_float to_chars() cannot parse this, which prevents roundtrip equivalence. I did not look further than that into this aspect.

Other than that, the proposed JSON strings .nan, .inf and -.inf can be used say in JS to check for these special values, and ryml deserializes them to their proper values as well.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.57%. Comparing base (8ca4a03) to head (e721250).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #574      +/-   ##
==========================================
- Coverage   97.61%   97.57%   -0.04%     
==========================================
  Files          46       46              
  Lines       13651    13677      +26     
==========================================
+ Hits        13326    13346      +20     
- Misses        325      331       +6     

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[davidrudlstorfer]

@biojppm thanks for the nice fix and also big thanks for the tag. Nice that this is now working as expected :)

(@gilrrei now we can revert 4C-multiphysics/fourcipp#78 and 4C-multiphysics/fourcipp#85)