v3x - boolean schemas

[commonism]

as defined in
https://json-schema.org/draft/2020-12/json-schema-core#section-4.3.2

true: {}
false: {not: {}}

previously boolean schemas were restricted to additionalProperties and there was inconsistent support for the expanded version of boolean schemas

c.f. - swagger-api/swagger-parser#1770

[codecov]

Codecov Report

Attention: Patch coverage is 96.61017% with 2 lines in your changes missing coverage. Please review.

Project coverage is 94.21%. Comparing base (72cedc9) to head (e8bfe04).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
aiopenapi3/model.py	92.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #287      +/-   ##
==========================================
- Coverage   94.25%   94.21%   -0.04%     
==========================================
  Files          86       86              
  Lines        7235     7277      +42     
==========================================
+ Hits         6819     6856      +37     
- Misses        416      421       +5     

Flag	Coverage Δ
core	94.21% <96.61%> (-0.04%)	⬇️
tests	94.21% <96.61%> (-0.04%)	⬇️

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