Gemini: Adjust "low" and "medium" reasoning effort

[afirstenberg]

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Issue Content

Google's OpenAI compatibility supports reasoning effort with different values that we set them for.
Low = 1k
Medium = 8k

See https://ai.google.dev/gemini-api/docs/openai#thinking

@jacoblee93 - Please assign to me

[jacoblee93]

Thank you @afirstenberg!