feat: (re-)enable Databricks inference adapter

Databricks inference adapter was broken, would not start, see #3486

- remove deprecated completion / chat_completion endpoints
- enable dynamic model listing w/o refresh, listing is not async
- use SecretStr instead of str for token
- backward incompatible change: for consistency with databricks docs, env DATABRICKS_URL -> DATABRICKS_HOST and DATABRICKS_API_TOKEN -> DATABRICKS_TOKEN
- databricks urls are custom per user/org, add special recorder handling for databricks urls
- add integration test --setup databricks
- enable chat completions tests
- enable embeddings tests
- disable n > 1 tests
- disable embeddings base64 tests
- disable embeddings dimensions tests

note: reasoning models, e.g. gpt oss, fail because databricks has a custom, incompatible response format

test with: ./scripts/integration-tests.sh --stack-config server:ci-tests --setup databricks --subdirs inference --pattern openai

note: databricks needs to be manually added to the ci-tests distro for replay testing

llama_stack/providers/registry/inference.py

@@ -152,7 +152,7 @@ def available_providers() -> list[ProviderSpec]:
             api=Api.inference,
             adapter=AdapterSpec(
                 adapter_type="databricks",
-                pip_packages=[],
+                pip_packages=["databricks-sdk"],
                 module="llama_stack.providers.remote.inference.databricks",
                 config_class="llama_stack.providers.remote.inference.databricks.DatabricksImplConfig",
                 description="Databricks inference provider for running models on Databricks' unified analytics platform.",