tests/artifacts/PURPOSE

dirstate: remove need_delay logic

Now that all¹ stored mtime are non ambiguous, we no longer need to apply the `need_delay` step.
The need delay logic was not great are mtime gathered during longer operation
could be ambiguous but younger than the `dirstate.write` call time.

So, we don't need that logic anymore and can drop it

This make the code much simpler. The code related to the test extension faking
the dirstate write is now obsolete and associated test will be migrated as
follow up. They currently do not break.

[1] except the ones from `hg update`, but `need_delay` no longer help for them
either.

Differential Revision: https://phab.mercurial-scm.org/D11796

This directory is meant to cache artifacts useful for tests (such as bundle).

Those artifacts need to be cached because they are slow to regenerate on each
test but too large to be tracked within the repository. They are not expected
to change between each run and can be cached.

The `./scripts/` contains code to generate the artifact while the `cache`
directory contains resulting artifact.