Adds streaming, async, /v1/responses, and /v1/messages coverage for the
Together AI overhaul (#38233, #38248, #38230, #38265, #38275), plus the
legacy api.together.xyz host and TOGETHER_AI_API_BASE through
litellm.completion. Each new test fails under a one-line mutation of the
merged code.
Tools passed for Together models with no supports_function_calling entry in
model_prices_and_context_window.json were rejected with UnsupportedParamsError
by default and silently dropped under drop_params, which made models emit tool
calls as plain text. Fail open instead: pass tool params through with a warning
and let Together validate. Models the registry explicitly marks as not
supporting function calling keep the loud contract: raise by default, drop with
a warning under drop_params.
