Lib_scoru_wasm/Test: AST generators and printers

Context

This MR introduces test helpers for QCheck generators and pretty-printers for WASM AST elements. It's needed for testing module decoders/encoders in !5872 (merged).

Manually testing the MR

> dune exec  src/lib_scoru_wasm/test/test_scoru_wasm.exe  

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR