[native] Cache decrypted media
Summary:
This diff integrates media cache into app logic.
Test Plan: Sent some encrypted messages, then wiped state. Reopened the app - media are loading slowly. Exit and re-enter thread. The media should be displayed almost immediately
Reviewers: atul, marcin, kamil, ashoat
Reviewed By: ashoat
Subscribers: ashoat, tomek
Differential Revision: https://phab.comm.dev/D7254