Merge upstream/main and add ChatUsage cost fields to Python SDK

Resolve openapi conflict by taking main (ChatUsage already documents cost, is_byok, and cost_details). Add costdetails.py and wire ChatUsage so cost data is preserved through model_dump(), fixing OpenRouterTeam#65.

chore: sync from monorepo (OpenRouterTeam#61)

chore: sync from monorepo (OpenRouterTeam#49)

chore: sync from monorepo (OpenRouterTeam#36)

Bring project back to correct version number

fix: update OpenAPI spec with router field (OpenRouterTeam#32)

feat: fix types and add reasoning_details to chat responses (OpenRout…

…erTeam#27)

chore: regenerate Python SDK with updated OpenAPI spec (OpenRouterTea…

…m#26)

chore: regenerate Python SDK v0.1.1 with new overlays (OpenRouterTeam#23

)

chore: Python SDK updates and regeneration (OpenRouterTeam#24)