## Problem Description

When testing DeepSeek v4 official API calls, I observed that if `thinking` and `reasoning_effort` are not explicitly set, the model defaults to thinking mode (returns `reasoning_content`). However, when a user wants to completely disable thinking (i.e., `reasoning_effort = none`), they currently must manually add `"thinking": {"type": "disabled"}` to achieve the expected behavior.

This creates inconsistency and extra work for LiteLLM users who expect `reasoning_effort: none` to fully disable reasoning without needing to also set `thinking: disabled`. LiteLLM should automatically translate `reasoning_effort: none` into `thinking: {"type": "disabled"}` when calling the DeepSeek v4 API.

## Reproduction Steps

### Test 1: Explicit enable + high reasoning effort ```sh curl https://api.deepseek.com/chat/completions \ -H "Content-Type: application/json" \ -H "Authorization: Bearer ${DEEPSEEK_API_KEY}" \ -d '{ "model": "deepseek-v4-pro", "messages": [ {"role": "system", "content": "You are a helpful assistant."}, {"role": "user", "content": "Hello!"} ], "thinking": {"type": "enable"}, "reasoning_eff…