chore: require Node >=20.19, pin dev to Node 22

vitest 4 / vite 8 rely on require(esm), which is only default on Node
20.19+. Add an engines floor and an .nvmrc pinning the dev/CI runtime to
Node 22 LTS so the test suite runs without experimental flags.

Author: vveerrgg

.nvmrc

@@ -0,0 +1 @@
+22

package.json

@@ -30,6 +30,9 @@
     },
     "author": "Humanjava Enterprises Inc",
     "license": "MIT",
+    "engines": {
+        "node": ">=20.19"
+    },
     "dependencies": {
         "@scure/bip39": "^2.0.1",
         "async-mutex": "^0.5.0",