Lib_base: upgrade QCheck tests to QCheck2
Context
We are upgrading QCheck tests to QCheck2 with integrated shrinking: #1583. Some QCheck1 helpers remain since it is used in others libs, they will be upgraded at the same time.
Depends on !3657 (merged) for helpers function.
Manually testing the MR
$ dune runtest src/lib_base/test -f
Edited by Valentin Chaboche