Provide alternate backends that use different OCaml PBT libraries

[ngernest]

Although the property-based testing code derived by Mica currently uses Jane Street’s Core.Quickcheck
library, Mica’s design is library-agnostic. It would be nice if Mica had alternate backends that used different OCaml PBT libraries (e.g. QCheck, Bam and Popper).

In particular, it'd be nice to build on recent work that uses the Etna PBT evaluation platform (Shi et al, ICFP '23) to compare the efficacy of different OCaml PBT frameworks (see Nikhil Kamath's PLDI '24 SRC work).