Test suite: deterministic time, shared fixtures, misnamed tests, stricter pytest config

[allen0099]

Test suite cleanups.

Split into one sub-issue per pull request:

• Tests: control time instead of sleeping for TTLs #185
• Tests: clean up the state manager tests #186
• Tests: move shared session fixtures to tests/session/conftest.py #187
• Tests: exercise the deprecated SessionMiddleware through its public API #188
• Tests: tighten the pytest configuration #189

[allen0099]

All sub-issues are done: #185, #186, #187, #188, #189.