Dal: derive sandbox and test parameters from mainnet's

Context

This MR changes the default Dal parameters for sandbox and test (and derives the values from those of mainnet) -> first commit

The MR also extends Dal unit & pbt tests to run them with sandbox, test and mainnet parameters. --> second commit Commit moved to a separate MR: !6628 (merged)

The third commit is a simple refactoring/simplification of tests

Manually testing the MR

Quick\unit:

dune exec src/proto_alpha/lib_protocol/test/unit/main.exe  -- test "^\[Unit\] dal slot proof$"

Slow/pbt:

dune exec src/proto_alpha/lib_protocol/test/pbt/test_dal_slot_proof.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