isnan check in issymetric/ishermitian for Numbers

[jishnub]

The issymmetric condition for numbers currently checks that x == x. The only condition under which this won't hold is if isnan(x). We may therefore replace this check by isnan, which is inferred at compile time for most Number types.

Similarly, ishermitian(x) = x == conj(x) may be replaced by isreal(x) && issymmetric(x).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.89%. Comparing base (1f55352) to head (40d5a4f).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1435   +/-   ##
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  Coverage   93.89%   93.89%           
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  Files          34       34           
  Lines       15900    15900           
=======================================
  Hits        14929    14929           
  Misses        971      971           

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