test(langchain,partners): disable pytest-benchmark under xdist to silence PytestBenchmarkWarning (#37901)

Test targets run with `-n auto`, which makes `pytest-benchmark` (present
via `langchain-tests`) auto-disable itself and emit a
`PytestBenchmarkWarning` once per xdist worker. Passing
`--benchmark-disable` turns the plugin off explicitly so the warning
never fires, matching what `core` and `langchain_v1` already do.

## Changes
- Add `--benchmark-disable` to the `-n auto` test targets across
`langchain` (unit) and 14 partner packages' integration targets:
`anthropic`, `chroma`, `deepseek`, `exa`, `fireworks`, `groq`,
`huggingface`, `mistralai`, `nomic`, `ollama`, `openai`, `openrouter`,
`qdrant`, `xai`.
- Deliberately excluded `text-splitters` and `model-profiles`: their
`test` group doesn't install `pytest-benchmark`, so the flag would fail
with `unrecognized arguments`. Verified by importing the plugin under
each package's actual dependency group before editing.

libs/partners/openai/Makefile

@@ -25,7 +25,7 @@ test tests:
 	TIKTOKEN_CACHE_DIR=tiktoken_cache uv run --group test pytest $(PYTEST_EXTRA) --disable-socket --allow-unix-socket $(TEST_FILE)
 
 integration_test integration_tests:
-	uv run --group test --group test_integration pytest -v --tb=short -n auto $(TEST_FILE)
+	uv run --group test --group test_integration pytest -v --tb=short -n auto --benchmark-disable $(TEST_FILE)
 
 # Run VCR cassette-backed integration tests in playback-only mode (no API keys needed).
 # Catches stale cassettes caused by test input changes without re-recording.