feat!: OpenAPI 3.1 support, fixes #115

[danielgtaylor]

This PR implements OpenAPI 3.1 support by switching to https://github.com/pb33f/libopenapi as the underlying Golang OpenAPI library. Every effort is being made to make this a backward-compatible change, however it's possible something may break or change slightly. Included with this change are:

• Some improvements to example generation
• Grouping of responses with the same model (commonly found in error responses)
• Improved test coverage
• Basic support for allOf, anyOf, oneOf

Related upstream issues:

• Incorrect loading of object property named default pb33f/libopenapi#5
• MediaType example incorrectly uses low-level node reference pb33f/libopenapi#6
• feat: add extensions to info pb33f/libopenapi#7
• Problem getting schema default for scalar type pb33f/libopenapi#15
• fix: conditionally set min/max/multiple pb33f/libopenapi#16
• fix(high): load schema.Examples into []any pb33f/libopenapi#21
• Headers prefixed with X- are mistakenly ignored pb33f/libopenapi#24

[codecov]

Codecov Report

Merging #145 (c59001f) into main (e73c737) will increase coverage by 7.55%.
The diff coverage is 92.26%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #145      +/-   ##
==========================================
+ Coverage   66.22%   73.78%   +7.55%     
==========================================
  Files          22       22              
  Lines        2594     2823     +229     
==========================================
+ Hits         1718     2083     +365     
+ Misses        698      583     -115     
+ Partials      178      157      -21     

Impacted Files	Coverage Δ
cli/apiconfig.go	81.48% <ø> (ø)
cli/content.go	73.48% <0.00%> (-2.30%)	⬇️
cli/lexer.go	69.10% <0.00%> (-3.55%)	⬇️
cli/operation.go	77.77% <ø> (ø)
cli/param.go	88.31% <ø> (ø)
cli/api.go	49.59% <75.00%> (+<0.01%)	⬆️
openapi/openapi.go	88.91% <90.15%> (+36.43%)	⬆️
openapi/example.go	98.63% <98.54%> (+98.63%)	⬆️
cli/formatter.go	88.94% <100.00%> (ø)
openapi/schema.go	98.46% <100.00%> (+6.89%)	⬆️
... and 4 more

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[wdullaer]

This library returns errors for circular references here:

restish/openapi/openapi.go

Line 513 in c145bbb

result, errs := doc.BuildV3Model()

Restish then proceeds to panic on these.

Unfortunately this breaks restish for all our APIs :-(

Looking at the libopenapi source code, it seems like the circular reference errors can be detected with errors.Is. I would have to assess the impact on example generation.

[waldyrious]

For future reference, @wdullaer's comment above was addressed in pb33f/libopenapi#39 and then in #151, which has now been released in https://github.com/danielgtaylor/restish/releases/tag/v0.15.1.