chore(upm): release 0.2.1 and run split on macos host runner

Bump package to 0.2.1 (maintenance/publish, no API changes) and repoint
the Publish UPM workflow from ubuntu-latest to the macos host runner.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Packages/com.darkmattergameproduction.fonepay-unity/package.json

@@ -1,7 +1,7 @@
 {
   "name": "com.darkmattergameproduction.fonepay-unity",
   "displayName": "Fonepay Unity",
-  "version": "0.2.0",
+  "version": "0.2.1",
   "unity": "6000.4",
   "unityRelease": "5f1",
   "description": "Fonepay payment integration for Unity. Generate Fonepay QR codes, await payment confirmation via websocket, and process tax refunds. Credentials managed via Tools > Fonepay > Settings.",