Add contracts gem support

[nepalez]

@mbj Possibly, you've already seen the contracts gem. What do you think of it? Are you planning to support it in future? (now using contracts makes method not recognizable by mutant).

[mbj]

@nepalez I like the concept of the gem. But I do not use it in a commercial environment. So I cannot support this on my OSS time.

This gem "likely" needs a custom injector, just like we have one for adamantium memoizers. I'm happy for someone doing a PR (I can help with pointing to the implemnetation vector), or funds this: I'd merge the feature.

Tagging as enhancement and not-on-authors-free-time.

[nepalez]

@mbj thank you. Now I'm stuck to other projects, maybe in September I could make a try

[mbj]

@nepalez For reference this is the current custom injection behavior for adamantium memoizers: https://github.com/mbj/mutant/blob/802e52338f5d6e2954a224e6f375a04c75527426/lib/mutant/subject/method/instance.rb#L30-L56

[dkubb]

Tagging as enhancement and not-on-authors-free-time.

@mbj you could rename the not-on-authors-free-time tag as needs-funding to be more precise about what you require to work on the issue.

[tjchambers]

@dkubb It would appear it needs funding or a PR. @mbj please correct?

[mbj]

@mbj you could rename the not-on-authors-free-time tag as needs-funding to be more precise about what you require to work on the issue.

Ack. I renamed to needs-funding-or-external-pr.

[tit]

+1, please add contract support for mutant. My project use gem contract on 100%? and I can use mutant-rspec for testing my test...

[mbj]

@tit I'd be happy to review a PR. Assuming the author of such a hypothetical PR would sign my CLA.

Its unlikely authorship to happen on my time at this point.