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

tests/integration/inference/test_openai_embeddings.py

@@ -41,6 +41,7 @@ def skip_if_model_doesnt_support_encoding_format_base64(client, model_id):
     provider = provider_from_model(client, model_id)
     if provider.provider_type in (
         "remote::together",  # param silently ignored, always returns floats
+        "remote::databricks",  # param silently ignored, always returns floats
     ):
         pytest.skip(f"Model {model_id} hosted by {provider.provider_type} does not support encoding_format='base64'.")
 
@@ -50,6 +51,8 @@ def skip_if_model_doesnt_support_variable_dimensions(client_with_models, model_i
     if provider.provider_type in (
         "remote::together",  # returns 400
         "inline::sentence-transformers",
+        # Error code: 400 - {'error_code': 'BAD_REQUEST', 'message': 'Bad request: json: unknown field "dimensions"\n'}
+        "remote::databricks",
     ):
         pytest.skip(
             f"Model {model_id} hosted by {provider.provider_type} does not support variable output embedding dimensions."
@@ -73,7 +76,6 @@ def skip_if_model_doesnt_support_openai_embeddings(client, model_id):
         "inline::meta-reference",
         "remote::bedrock",
         "remote::cerebras",
-        "remote::databricks",
         "remote::runpod",
         "remote::sambanova",
         "remote::tgi",