refactor(core): move models.dev into core (#27347)

packages/core/test/plugin/fixtures/provider-factory.ts

@@ -0,0 +1,9 @@
+export function createFixtureProvider(options: Record<string, unknown>) {
+  const captured = Object.fromEntries(Object.entries(options))
+  return Object.assign((modelID: string) => ({ modelID, options: captured }), {
+    options: captured,
+    languageModel(modelID: string) {
+      return { modelID, options: captured }
+    },
+  })
+}