Closing multiple toasts in a single frame panics

[tvolk131]

Currently we close toasts by their index in the toasts array. This works fine unless we're closing multiple toasts within one update call, in which case the first toast will be closed correctly, but the index of all subsequent toasts will be 1 less than before when processing other toast close events. This results in incorrect toasts being closed or, even more problematically, the following code panicking since we're calling Vec::remove() on an index that no longer exists:

keystache/src/app.rs

Lines 146 to 150 in b844ad4

	Message::CloseToast(index) => {
	self.toasts.remove(index);
	Task::none()
	}

Toast closing should be idempotent and order-independent. The easiest way to achieve this would be to add a UUID to each toast, and on close, filter toasts excluding that UUID rather than removing by exact index.