Remove (or at least mitigate) shadowing of `input` within the OpenAI integration

[ericapisani]

There's a number of places where we name variables input (such as in `_calculate_responses_token_usage`) that reflect the OpenAI variable names, but that cause shadowing of the input Python function.

We should look to rename these variables to avoid this.

[linear-code]

PY-2275