Build: remove ocamlformat dep for runtest

Context

The goal of the MR is to get rid of the ocamlformat dependency when building the runtest alias. We can leave without ocamlformat for generated tests files. This MR also includes a small refactoring / cleanup of the time_measurement test infra

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