Migrate from JavaScript to TypeScript

Convert all 16 source files from .js to .ts with full type annotations.
Add types.ts with interfaces for all data structures. Export BufferReader
and BufferWriter from index. Use 'as const' for literal types on constants.

package.json

@@ -2,15 +2,22 @@
   "name": "@liamcottle/meshcore.js",
   "version": "1.11.0",
   "description": "",
-  "main": "src/index.js",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
   "type": "module",
   "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "build": "tsc",
+    "prepublishOnly": "npm run build"
   },
+  "files": ["dist"],
   "author": "Liam Cottle <liam@liamcottle.com>",
   "license": "MIT",
   "dependencies": {
     "@noble/curves": "^1.8.1",
     "serialport": "^13.0.0"
+  },
+  "devDependencies": {
+    "@types/node": "^22.0.0",
+    "typescript": "^5.7.0"
   }
 }