feat(react): add referentially-stable snapshot and selector caches

useSyncExternalStore requires getSnapshot to return an identical
reference when unchanged; @wrnexus/store's readonlySnapshot returns a
fresh clone per call. The cache lives here rather than in the store
package so existing consumers are untouched.

createSelectorCache takes an optional equality function: the Object.is
default can never stabilize a selector that allocates, which is the
usual source of infinite re-renders.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/react/package.json

@@ -0,0 +1,25 @@
+{
+  "name": "@wrnexus/react",
+  "version": "0.8.8",
+  "type": "module",
+  "main": "src/index.ts",
+  "exports": {
+    ".": "./src/index.ts",
+    "./runtime": "./src/runtime-source.ts"
+  },
+  "peerDependencies": {
+    "react": "^19.0.0",
+    "react-dom": "^19.0.0"
+  },
+  "peerDependenciesMeta": {
+    "react": { "optional": true },
+    "react-dom": { "optional": true }
+  },
+  "dependencies": {
+    "@wrnexus/store": "workspace:*"
+  },
+  "devDependencies": {
+    "@types/bun": "^1.3.14",
+    "typescript": "^6.0.3"
+  }
+}