test(logging): port logging tests to pytest style

Rewrite the logging test suite from unittest.TestCase into pytest-style
test classes with plain assert statements, fixtures, and section banners.

All rigorous, mutation-verified assertions are preserved: the Slack test
pins the concrete chat.postMessage endpoint rather than driver.slack_url
(which would be circular), and the daily-file test proves the on-disk file
name follows the configured timezone by inspecting real files.

The two weak tests are intentionally not carried over: the tautological
daily 'different date' test that compared two self-built string literals,
and the Slack circular self-reference assertion.

Author: tmgbedu