[ add ] clean version of Data.Fin.Properties.searchMinimalCounterexample

[jamesmckinna]

Revised version of the relevant code from #2744 incorporating:

• MinimalCounterexample now a record
• infix versions now as (duplicate) definitions of the verbose CamelCase versions, not as syntax
• use of inject deprecated in favour of _<_; add inject-< as lemma to smooth the path

[JacquesCarette]

I like all of this, except for the name μ. It's a cute pun, but caters to a rather small crowd.

How about calling the constructor least instead? If you want a pun, then μ⟨_⟩ can be called the-least. I don't think μ⟨¬_⟩ passes the Fairbairn threshold.