chore: require pnpm >=10 in engines

pnpm 9 reached end-of-life; align `engines.pnpm` with the pinned
packageManager so older pnpm gets rejected on install rather than
failing later with cryptic lockfile errors.

Author: lutter

package.json

@@ -13,8 +13,9 @@
   "private": true,
   "engines": {
     "node": ">=20.0.0",
-    "pnpm": "9"
+    "pnpm": ">=10"
   },
+  "packageManager": "pnpm@10.17.1",
   "scripts": {
     "build": "pnpm --filter=@graphprotocol/graph-* build",
     "lint": "pnpm lint:prettier && pnpm lint:eslint",