Fix AsyncToSync error in Databricks deferrable operators by fetching connection asynchronously

[saitejabandaru-in]

Closes #71525.

Motivation

When DatabricksRunNowOperator(deferrable=True) is used, the triggerer executes DatabricksExecutionTrigger.run(). Inside the async loop, the trigger polls for status via DatabricksHook.a_get_run_state(), which eventually calls self._endpoint_url(). That function tries to read self.databricks_conn, which is a @cached_property invoking self.get_connection().

In Airflow 3 (TaskSDK), get_connection bridges to a synchronous supervisor call using async_to_sync. Because this happens inside the triggerer's already-running asyncio loop, it crashes with RuntimeError: You cannot use AsyncToSync in the same thread as an async event loop.

Changes

• Added adatabricks_conn to BaseDatabricksHook which fetches the connection asynchronously via aget_connection.
• Added ahost, _a_endpoint_url, and _a_get_oidc_token_service_url to prevent async methods from calling self.host (which also evaluates databricks_conn synchronously).
• Refactored all async def methods in BaseDatabricksHook to use (await self.adatabricks_conn()) and await self._a_endpoint_url().
• Updated unit tests to mock adatabricks_conn.