(Refactor) Code Quality improvement - Use Common base handler for Cohere /generate API (#7122)

* use validate_environment in common utils

* use transform request / response for cohere

* remove unused file

* use cohere base_llm_http_handler

* working cohere generate api on llm http handler

* streaming cohere generate api

* fix get_model_response_iterator

* fix streaming handler

* fix get_model_response_iterator

* test_cohere_generate_api_completion

* fix linting error

* fix testing cohere raising error

* fix get_model_response_iterator type

* add testing cohere generate api

litellm/main.py

@@ -109,7 +109,6 @@ from .llms.azure_text import AzureTextCompletion
 from .llms.bedrock.chat import BedrockConverseLLM, BedrockLLM
 from .llms.bedrock.embed.embedding import BedrockEmbedding
 from .llms.bedrock.image.image_handler import BedrockImageGeneration
-from .llms.cohere.completion import completion as cohere_completion  # type: ignore
 from .llms.cohere.embed import handler as cohere_embed
 from .llms.custom_httpx.llm_http_handler import BaseLLMHTTPHandler
 from .llms.custom_llm import CustomLLM, custom_chat_llm_router
@@ -446,6 +445,7 @@ async def acompletion(
             or custom_llm_provider == "groq"
             or custom_llm_provider == "nvidia_nim"
             or custom_llm_provider == "cohere_chat"
+            or custom_llm_provider == "cohere"
             or custom_llm_provider == "cerebras"
             or custom_llm_provider == "sambanova"
             or custom_llm_provider == "ai21_chat"
@@ -1895,31 +1895,22 @@ def completion(  # type: ignore # noqa: PLR0915
             if extra_headers is not None:
                 headers.update(extra_headers)
 
-            model_response = cohere_completion.completion(
+            response = base_llm_http_handler.completion(
                 model=model,
+                stream=stream,
                 messages=messages,
+                acompletion=acompletion,
                 api_base=api_base,
                 model_response=model_response,
-                print_verbose=print_verbose,
                 optional_params=optional_params,
                 litellm_params=litellm_params,
-                logger_fn=logger_fn,
-                encoding=encoding,
+                custom_llm_provider="cohere",
+                timeout=timeout,
                 headers=headers,
+                encoding=encoding,
                 api_key=cohere_key,
                 logging_obj=logging,  # model call logging done inside the class as we make need to modify I/O to fit aleph alpha's requirements
             )
-
-            if "stream" in optional_params and optional_params["stream"] is True:
-                # don't try to access stream object,
-                response = CustomStreamWrapper(
-                    model_response,
-                    model,
-                    custom_llm_provider="cohere",
-                    logging_obj=logging,
-                )
-                return response
-            response = model_response
         elif custom_llm_provider == "cohere_chat":
             cohere_key = (
                 api_key