fix(tests): shim removed aiohttp stream mixin for vcr

VCR.py imports aiohttp.streams.AsyncStreamReaderMixin at module import time, but newer aiohttp releases removed that internal symbol. Add a no-op compatibility shim before importing the aiohttp stubs so provider test collection does not fail.

Author: AbhiPrasad

py/src/braintrust/conftest.py

@@ -32,6 +32,14 @@ def _patch_vcr_aiohttp_stubs():
     See: https://github.com/kevin1024/vcrpy/issues/927
     """
     try:
+        from aiohttp import streams
+
+        # VCR.py imports this aiohttp internals symbol at module import time, but
+        # newer aiohttp releases removed it. Provide a no-op compatibility shim
+        # before importing vcr.stubs.aiohttp_stubs so test collection does not fail.
+        if not hasattr(streams, "AsyncStreamReaderMixin"):
+            setattr(streams, "AsyncStreamReaderMixin", object)
+
         from vcr.stubs import aiohttp_stubs
     except ImportError:
         return