Speed up DS unit test.

[anoto-moniz]

Have requests in test_design_space_limits return smaller responses, as most of the time was spent building them into objects.

PR Type:

• Breaking change (fix or feature that would cause existing functionality to change)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Maintenance (non-breaking change to assist developers)

Adherence to team decisions

• I have added tests for 100% coverage
• I have written Numpy-style docstrings for every method and class.
• I have communicated the downstream consequences of the PR to others.
• I have bumped the version in __version__.py

[kroenlein]

This dramatically reduces the entropy in this test, but I was always skeptical that we needed that much.

Pulling in numpy would also speed this up (https://numpy.org/doc/stable/reference/random/generated/numpy.random.rand.html), but probably doesn't matter.