LiteLLM copies every upstream response header onto its own response prefixed
'llm_provider-'. For our providers that hands callers operational detail about the
co-op's own account — verified live: llm_provider-x-credits-remaining carried the
remaining provider balance in every member's response.
Build-time patch makes _get_llm_provider_headers() return {}. The four OpenAI-style
x-ratelimit-* headers a provider may send are still forwarded: those describe the
caller's own request, not the co-op's account.
