De-dupe messages properly

[HarryET]

We shouldn't reject if we already stored a notification, we should check if the notification exists and if it does see if this notification has been processed before, if so: return 200 early else continue with normal processing and store the notification after we have processed to prevent duplicates.

[chris13524]

Some work will be required to identity and differentiate between a temporary provider error (e.g. failed network request), and permanent ones, so that permeant ones aren't unnecessarily retried. Some initial work here: https://walletconnect.slack.com/archives/C03SPNLG39P/p1696087208180819