Refactor SubAccountUI for async loading and caching

Reworked SubAccountUI to load accounts and update overview statistics asynchronously using ThreadPoolExecutor, improving UI responsiveness. Added price caching and batch price updates to reduce API calls and speed up account value calculations. Updated asset dropdown and account details to refresh asynchronously, and ensured proper thread cleanup on exit. Bumped version to 2.1.3 in settings.yaml.

Author: GoneInactive

resources/data/settings/settings.yaml

@@ -1,4 +1,4 @@
 program:
   name: "TradeByte"
-  version: "2.1.2"
+  version: "2.1.3"
   debug: false