@langchain/google: Add integration tests for `codeExecution`

[afirstenberg]

Privileged issue

• I am a LangChain maintainer, or was asked directly by a LangChain maintainer to create an issue here.

Issue Content

See #10071 for sample code from kyrisu (@kyrisu) that should be turned into a test case.
Test code execution, both streamed and non-streamed.

Hunter Lovell (@hntrl) - Please assign to me.