test: reset intentservice state between tests

[lorenzozanee]

What

intentservice keeps its state in module globals (is_loaded, intent_typology, intent_detectors, intents_active) and nothing resets them between tests. The suite runs in a single process, so whichever test last called load() decides what every later test sees. This is the same problem langservice had, already fixed by clear_langprovider_state in tests/langservice/conftest.py; intentservice still needs the equivalent.

Concrete symptom: test_invalid_intents_rejected never loads the service itself, so it only passes because an earlier test leaves the service loaded — run alone it raises GarakException: get_intent_stubs called on non-loaded intentservice instead of the expected ValueError. Intent-probe translation tests in tests/langservice/probes/test_probes_base.py also flip their skip reason depending on whether an earlier test loaded the service. (The issue's example uses probes.tap.TAPIntent, which no longer exists on main; the same flip reproduces with the remaining IntentProbe, probes.grandma.GrandmaIntent.)

Fix

• autouse clear_intentservice_state fixture in tests/conftest.py, mirroring clear_langprovider_state: resets the four module globals after every test
• test_invalid_intents_rejected now loads the service itself instead of relying on leaked state
• new regression pair in tests/cas/test_intentservice_state_reset.py: the first test loads the service and asserts it is populated, the second asserts the state was reset in between — the second test fails on main without the fixture

I searched the open PRs and none address intentservice test state; the only intentservice-flavoured open PR (#2030) is about harness intent handling.

Verification

python -m pytest tests/cas tests/test_payloads.py tests/harnesses/test_harness_intent_plugin_cache.py -q
337 passed, 1 skipped

python -m pytest tests/cas/test_intentservice_state_reset.py -v
2 passed   (without the fixture the second test fails on main:
            AssertionError: intentservice must not stay loaded across tests)

# order independence, previously inconsistent:
python -m pytest -p no:cacheprovider "tests/cas/test_intentservice.py::test_load_intentservice" "tests/langservice/probes/test_probes_base.py::test_probe_prompt_translation[probes.grandma.GrandmaIntent]" -rs
python -m pytest -p no:cacheprovider "tests/langservice/probes/test_probes_base.py::test_probe_prompt_translation[probes.grandma.GrandmaIntent]" "tests/cas/test_intentservice.py::test_load_intentservice" -rs
both orders now skip with the same reason; before the change the skip reason flipped

• Verify the thing does what it should
• Verify the thing does not do what it should not

Closes #2124

[jmartin-tech]

There is no reason to have a test file to test testing only functionality.

At best test_intentservice_load_populates_state asserts are functionality that should be added to test_load_intentservice in test_intentservice.py.

[jmartin-tech]

Setting this to autouse at the root of the test path will cause it to run for every test. Is that really what it should do?