0.42.0

(feat): Wire up OAuth client-credentials authentication in the generated client. When an OAuth client-credentials scheme is defined, the generated ClientConfig now carries the resolved token endpoint and the HttpClient automatically fetches, caches, and refreshes a bearer token before making authenticated requests. Previously the OAuth scaffolding was present but never connected to the request flow.

The token exchange now honors the token endpoint’s configured request/response property mapping instead of a hardcoded client_id/client_secret/grant_type shape: the request body is built from the configured property names (e.g. camelCase clientId/clientSecret), literal properties such as grant_type are only sent when the contract declares them, and the access token / expiry are read from the configured response property names.