fix: avoid "double proxying"

This can be reverted when the following PR is merged: pmndrs/valtio#1038

src/index.ts

@@ -1,6 +1,5 @@
 export {
   getVersion,
-  proxy,
   ref,
   snapshot,
   type INTERNAL_Op,
@@ -22,3 +21,4 @@ export {
   type ReactiveClass,
   type ReactiveProxy,
 } from './runtime/instance'
+export { proxy } from './runtime/proxy'

src/runtime/proxy.ts

@@ -0,0 +1,10 @@
+import { proxy as createProxy, unstable_getInternalStates } from 'valtio'
+
+const { proxyStateMap } = unstable_getInternalStates()
+
+export function proxy<T extends object>(data: T): T {
+  if (proxyStateMap.has(data)) {
+    return data
+  }
+  return createProxy(data)
+}