v0.21.2

• Add --android-adaptive-icon-background to flet build command.
• Fix for mobile Safari: Store session ID in SessionStorage instead of window.name.
• Fix _FletSocketServer__receive_loop_task error on Linux.
• Replace deprecated (in Python 3.12) datetime.utcnow() with datetime.now(timezone.utc).
• Fix a call to self.__executor.shutdown for Python 3.8.
• Add client IP and user agent to a session ID.
• Generate crypto-strong strings across the framework.