Improve processing of `content` argument that's passed in to `generate_content` method

While working through [PY-2287](https://linear.app/getsentry/issue/PY-2287/fix-failing-checkbinaryredaction-assertion-in-the-vision-llm-test-ai), it looks like there may be a few gaps here.

Audit the following to ensure that we have complete coverage of these data types:

* `FileDict`
* `PartDict` forms that involve `file_data`, `function_call`, `executable_code`, and `code_execution_result`