improve support for custom Number types

[aplavin]

Some common number types subtype <: Number and not <: Real, while being real-like underneath sometimes. Here, we fix/generalize "realness" checks to make them correct for such number types.

Tests use Unitful as an example of a <: Number type. For example, functions like x^2 and x^3 are now invertible for unitful x.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.24%. Comparing base (1d4cbb7) to head (7086087).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #50      +/-   ##
==========================================
- Coverage   99.27%   99.24%   -0.03%     
==========================================
  Files           6        6              
  Lines         137      132       -5     
==========================================
- Hits          136      131       -5     
  Misses          1        1              

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[aplavin]

done that + bumped version in Project.toml

[oschulz]

Looks good to me - any objections, @devmotion ?

[oschulz]

JuliaRegistries/General#111164