Tests: Run DAL tests on less configs to reduce CI time

Context

MR !6628 (merged) refactored DAL pbt & unit tests to run them with mainnet, test and sandbox parameters. However, they now take a lot of CI time because of the underlying crypto.

This MR replaces the "mainnet, test and sandbox parameters" by just one custum-net parameters whose (small) parameters are derived from those of mainnet.

Manually testing the MR

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