[Perf][CI] Reuse the Whisper judge worker across a test module (#6208)

Signed-off-by: Shenglei Fu <sfu@confluent.io>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

tests/helpers/fixtures/media.py

@@ -0,0 +1,24 @@
+"""Fixtures for the reused Whisper transcription worker."""
+
+import sys
+
+import pytest
+
+
+@pytest.fixture(autouse=True, scope="module")
+def release_audio_transcriber_after_module():
+    """Free the transcription worker's device memory once a test module is done.
+
+    A backstop. The server and runner fixtures already release the worker when
+    each of their instances tears down, which is what keeps Whisper off the
+    device while the next parametrized server initializes. This covers the
+    remaining case: a module that transcribes without using those fixtures.
+
+    Reached through ``sys.modules`` because ``tests/conftest.py`` deliberately
+    keeps ``tests.helpers.media`` lazy: a module that never transcribed should
+    not pay to import it.
+    """
+    yield
+    media = sys.modules.get("tests.helpers.media")
+    if media is not None:
+        media.release_audio_transcriber()