[ damus-io/damus ] Move profile update handling from notes to the background
During profiling, I found that some large hangs were being caused by a
large number of `notify` calls (and their handling functions) keeping
the main thread overly busy.
We cannot move the `notify` mechanism to a background thread (It has to
be done on the main actor or else runtime warnings/errors appear), so
instead this commit removes a very large source of notify calls/handling around
NoteContentView, and replaces it with a background task that streams