Refactor providerCost to read `usage.raw.cost_details.upstream_inference_cost`,
which both `@ai-sdk/anthropic` (`convertAnthropicUsage`) and `@ai-sdk/openai`
(`convertOpenAIResponsesUsage`) populate with the verbatim OpenRouter usage
object. This unifies the Anthropic Messages and OpenAI Responses cost paths
through a single branch and removes the redundant `metadata.anthropic.usage`
branch (the SDK exposes the same data under both keys for Anthropic, and only
under `raw` for Responses).
kiloconnect[bot]
c8073d9014