* test(tests): add unit testing for litellm_proxy integration
* fix(cost_calculator.py): fix tracking cost in sdk when calling proxy
* fix(main.py): respect litellm.api_base on `vertex_ai/` and `gemini/` routes
* fix(main.py): consistently support custom api base across gemini + vertexai on embedding + completion
* feat(vertex_ai/): test
* fix: fix linting error
* test: set api base as None before starting loadtest
* use vertex llm as base class for embeddings
* use correct vertex class in main.py
* set_headers in vertex llm base
* add types for vertex embedding requests
* add embedding handler for vertex
* use async mode for vertex embedding tests
* use vertexAI textEmbeddingConfig
* fix linting
* add sync and async mode testing for vertex ai embeddings
* add basic load test
* add vertex ai load test on ci cd
