Fix issues in existing tests

[daniel-k]

Some tests are flaky. This fixes an issue encountered in a recent CI build as well as a local test failure of Hypothesis.

• Fix performance of test__get_timeseries_raises_on_mixed_response() resulting in Hypothesis health check error
• Fix datetime strategies that can result in the same timestamp, throwing off tests that assert start != end

[github-actions]

Coverage results

This is the coverage report for commit b191ec1

Name                                                                                Stmts   Miss  Cover   Missing
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.tox/py/lib/python3.12/site-packages/enlyze/__init__.py                                 4      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/base.py                        70      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/production_runs/client.py      20      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/production_runs/models.py      52      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/timeseries/client.py           19      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/timeseries/models.py           44      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/auth.py                                    13      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/client.py                                 108      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/constants.py                                8      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/errors.py                                   3      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/iterable_tools.py                           7      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/models.py                                 110      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/schema.py                                  26      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/validators.py                              38      0   100%
-----------------------------------------------------------------------------------------------------------------
TOTAL                                                                                 522      0   100%

4 empty files skipped.