lib_proxy/shell_services: upgrade qcheck to qcheck2

Context

We are upgrading QCheck tests to QCheck2 which bring automatic shrinking.

Part of #1583

Some generators were reduced due to execution time (e.g. string becomes small_string), we now have:

• test_fuzzing_proxy_getter: master: ~25sec; now: ~35sec
• test_fuzzing_light: master: ~65sec; now: ~100sec

The tests used a lot of list and string generators so this regression is not surprising .

Manually testing the MR

Checklist

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