feat: Add ExternalRuntimeOptions to BigQuery routine

[google-labs-jules]

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.

Fixes #2240
Replaces PR #2305

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PR created automatically by Jules for task 17042493298890483722

[google-labs-jules]

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[chalmerlowe]

Jules:

We lack some coverage via unit tests.
Coverage indicates that we don't have coverage on lines 375-380, 816-818, 908, and 912. Please see what you can do to update the test suite.

[google-labs-jules]

Jules:

We lack some coverage via unit tests.
Coverage indicates that we don't have coverage on lines 375-380, 816-818, 908, and 912. Please see what you can do to update the test suite.

I have added new unit tests to cover the missing lines of code. The test suite now passes with 100% coverage for the new functionality.

[chalmerlowe]

Jules:

PyType is making guesses about the types of some objects in the routine.py file.

Here are two examples.

/tmpfs/src/github/python-bigquery/google/cloud/bigquery/routine/routine.py:834:1: error: in container_memory: bad option 'int' in return type [bad-return-type]
           Expected: Optional[str]
  Actually returned: Optional[Any]

        return self._properties.get("containerMemory")~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        return self._properties.get("containerMemory")


/tmpfs/src/github/python-bigquery/google/cloud/bigquery/routine/routine.py:856:1: error: in runtime_connection: bad option 'int' in return type [bad-return-type]
           Expected: Optional[str]
  Actually returned: Optional[Any]

        return self._properties.get("runtimeConnection")~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        return self._properties.get("runtimeConnection")

Any suggestions?

[google-labs-jules]

Jules:

PyType is making guesses about the types of some objects in the routine.py file.

Here are two examples.

/tmpfs/src/github/python-bigquery/google/cloud/bigquery/routine/routine.py:834:1: error: in container_memory: bad option 'int' in return type [bad-return-type]
           Expected: Optional[str]
  Actually returned: Optional[Any]

        return self._properties.get("containerMemory")~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        return self._properties.get("containerMemory")


/tmpfs/src/github/python-bigquery/google/cloud/bigquery/routine/routine.py:856:1: error: in runtime_connection: bad option 'int' in return type [bad-return-type]
           Expected: Optional[str]
  Actually returned: Optional[Any]

        return self._properties.get("runtimeConnection")~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        return self._properties.get("runtimeConnection")

Any suggestions?

I have applied the suggested changes to address the type-checking errors. The tests all pass, and the code should now be free of any type-related issues.

[Linchin]

I wonder if this is necessary?

[Linchin]

Approved with a minor comment

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