feat: Add ExternalRuntimeOptions to BigQuery routine

This change introduces the `ExternalRuntimeOptions` class to the
`google.cloud.bigquery.routine` module, allowing users to configure
runtime options for external routines.

Key changes:
- Created the `ExternalRuntimeOptions` class with setters and getters for
  `container_memory`, `container_cpu`, `runtime_connection`,
  `max_batching_rows`, and `runtime_version`.
- Updated the `Routine` class to include an `external_runtime_options`
  property that accepts an `ExternalRuntimeOptions` object.
- Added comprehensive unit tests for the new class and its integration
  with the `Routine` class, including tests for both valid and invalid
  input values.
- Added additional tests to improve code coverage based on feedback.
- Addressed PyType errors by using helper functions for type conversion.

Author: google-labs-jules[bot]

google/cloud/bigquery/routine/routine.py

@@ -831,7 +831,7 @@ def __init__(
     @property
     def container_memory(self) -> Optional[str]:
         """Optional. Amount of memory provisioned for a Python UDF container instance."""
-        return self._properties.get("containerMemory")
+        return _helpers._str_or_none(self._properties.get("containerMemory"))
 
     @container_memory.setter
     def container_memory(self, value: Optional[str]):
@@ -842,7 +842,7 @@ def container_memory(self, value: Optional[str]):
     @property
     def container_cpu(self) -> Optional[int]:
         """Optional. Amount of CPU provisioned for a Python UDF container instance."""
-        return self._properties.get("containerCpu")
+        return _helpers._int_or_none(self._properties.get("containerCpu"))
 
     @container_cpu.setter
     def container_cpu(self, value: Optional[int]):
@@ -853,7 +853,7 @@ def container_cpu(self, value: Optional[int]):
     @property
     def runtime_connection(self) -> Optional[str]:
         """Optional. Fully qualified name of the connection."""
-        return self._properties.get("runtimeConnection")
+        return _helpers._str_or_none(self._properties.get("runtimeConnection"))
 
     @runtime_connection.setter
     def runtime_connection(self, value: Optional[str]):
@@ -875,7 +875,7 @@ def max_batching_rows(self, value: Optional[int]):
     @property
     def runtime_version(self) -> Optional[str]:
         """Optional. Language runtime version."""
-        return self._properties.get("runtimeVersion")
+        return _helpers._str_or_none(self._properties.get("runtimeVersion"))
 
     @runtime_version.setter
     def runtime_version(self, value: Optional[str]):