Add TypeScript type declarations

- Add index.d.ts with comprehensive type definitions for all exported classes
- Include type declarations for Connection, NodeJSSerialConnection, and other connection types
- Add types for Constants, Advert, Packet, BufferUtils, and CayenneLpp
- Add type declarations for submodules (constants, buffer_reader, buffer_writer)
- Update package.json to reference the types file

This enables TypeScript users to have proper type checking and autocomplete when using the library.

package.json

@@ -3,6 +3,7 @@
   "version": "1.10.0",
   "description": "",
   "main": "src/index.js",
+  "types": "index.d.ts",
   "type": "module",
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1"