Massive refactor of API

- Switch to function based API
- Anthropic SDK style async generator
- Fully typed with escape hatches for custom models

biome.json

@@ -28,6 +28,6 @@
 		"lineWidth": 120
 	},
 	"files": {
-		"includes": ["packages/*/src/**/*", "*.json", "*.md"]
+		"includes": ["packages/*/src/**/*", "packages/*/test/**/*", "*.json", "*.md"]
 	}
 }