Small fixes and make the project compile with ocaml 5.1

[FardaleM]

This is a collection of small fixes that I have found so far.

• add the dependency to the project to be able to opam install it
• correct the compilation with ocaml 5.1 because of change in the compiler libs
• correct the implementation of subset in the bitvector implementation

[FardaleM]

It is still not compiling, don't merge.

[FardaleM]

Now, it compiles, but the second commit needs to be checked.