Fix caplog handler level restoration (swev-id: pytest-dev__pytest-7571)

[casey-brooks]

Summary

• ensure the shared caplog handler is reset to NOTSET when no global log level is configured
• add regression tests covering handler level restoration across default, logger-specific, and nested overrides
• fixes caplog fixture doesn't restore log level after test (regression in 6.0) #35

Observed Failure and Reproduction

• on the base branch, create two tests where the first calls caplog.set_level(42) and the second asserts caplog.handler.level == logging.NOTSET
• the second test inherits level 42 from the previous run, causing assertions and log capture expectations to fail without any stack trace (state leakage only)

Testing

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest testing/logging/test_fixture.py
• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest testing/logging
• .venv/bin/flake8 src/_pytest/logging.py testing/logging/test_fixture.py

[casey-brooks]

Local Validation

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest testing/logging/test_fixture.py
• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest testing/logging
• .venv/bin/flake8 src/_pytest/logging.py testing/logging/test_fixture.py

[noa-lucent]

Resetting the shared caplog handler before every phase breaks callers that configure logging during setup; please limit the reset to the first phase (setup) and cover the scenario with a regression test.

[noa-lucent]

[major] Resetting the shared handler unconditionally here runs on every phase (setup/call/teardown). That wipes out levels a test deliberately applies earlier in the same test, for example a fixture that calls during setup so the test body runs with that filtering. On the base branch that works because the handler keeps the level until finalization; with this change the call phase starts at , so those fixtures silently lose their effect. Please gate the reset so it only runs for the first phase of each test (e.g. ), and add a regression test covering a fixture that calls during setup to prove the level remains active for the test body.}

[casey-brooks]

Local Validation (update)

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest testing/logging/test_fixture.py (18 passed)
• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest testing/logging (61 passed)
• .venv/bin/flake8 src/_pytest/logging.py testing/logging/test_fixture.py

[noa-lucent]

Looks good. Resetting only during setup preserves fixture-configured levels, and the added regression test covers that scenario alongside the broader handler restoration cases.