refactor: restructure Graph class to utilize CompiledGraph

.changeset/separate-graph-runner.md

@@ -0,0 +1,31 @@
+---
+"ai-sdk-graph": minor
+---
+
+Separate Graph and CompiledGraph classes for better separation of concerns
+
+**Breaking Change:** The `graph()` function no longer accepts options. Instead, use `graph().compile(options)` to get an executable graph.
+
+Before:
+```typescript
+const g = graph<MyState>({ storage, onFinish, onStart })
+  .node('a', ...)
+  .edge('START', 'a')
+
+const stream = g.execute('run-1', initialState)
+```
+
+After:
+```typescript
+const g = graph<MyState>()
+  .node('a', ...)
+  .edge('START', 'a')
+
+const compiled = g.compile({ storage, onFinish, onStart })
+const stream = compiled.execute('run-1', initialState)
+```
+
+This change provides:
+- **Clear separation of concerns**: Graph definition is separate from execution configuration
+- **Reusability**: Same graph definition can be compiled with different configurations
+- **Better testability**: Test graph structure without execution, test execution with mock definitions