Update deepseek api_base url to current production endpoint - https://api.deepseek.com/v1

[oldheadsouf]

Title

Replace beta endpoint with production endpoint as default api_base url

Relevant issues

Issue #15986

Pre-Submission checklist

Please complete all items before asking a LiteLLM maintainer to review your PR

• [ X] I have Added testing in the tests/litellm/ directory, Adding at least 1 test is a hard requirement - see details
• I have added a screenshot of my new test passing locally
• [ X] My PR passes all unit tests on make test-unit
• [X ] My PR's scope is as isolated as possible, it only solves 1 specific problem

Type

🐛 Bug Fix

Changes

Changed Deepseek default api_base url from beta endpoint to documented production endpoint and updated corresponding unit test.

• This is the official production endpoint according to current Deepseek documentation

• Using the documented production API is the sane default over an experimental and poorly documented beta endpoint. It is not clear that the beta endpoint serves the latest models or is feature complete

• The header text of llms/deepseek/chat/transformation.py already states the proper production endpoint is in use https://github.com/oldheadsouf/litellm/blob/2a18b29c9caa3f5dc5cf60eee347827adefb6805/litellm/llms/deepseek/chat/transformation.py#L2

Note: the v1 has no relationship with model version

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[krrishdholakia]

Hi @oldheadsouf is there any loss of functionality with this change?