v1.9.0: chore: replace go-chi/cors with stdlib-only CORS implementation

- Remove dependencies on go-chi/chi/v5, go-chi/cors, and go-chi/httprate
- Implement custom CORS middleware matching go-chi/cors API and behavior
- Add CORSOptions struct mirroring go-chi/cors.Options for drop-in replacement
- Support wildcard origin matching with prefix/suffix pattern validation
- Implement proper preflight and actual request handling per CORS spec
- Add origin, method, and header validation with case normalization
- Handle