Stream from both NDB and network relays

This commit takes a step back from the full local relay model by
treating NostrDB as one of the many relays streamed from, instead of the
one exclusive relay that other classes rely on.

This was done to reduce regression risk from the local relay model
migration, without discarding the migration work already done.

The full "local relay model" behavior (exclusive NDB streaming) was
hidden behind a feature flag for easy migration later on.

Closes: https://github.com/damus-io/damus/issues/3225
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>

damusTests/NostrNetworkManagerTests/NostrNetworkManagerTests.swift

@@ -21,7 +21,7 @@ class NostrNetworkManagerTests: XCTestCase {
         let notesJSONL = getTestNotesJSONL()
 
         for noteText in notesJSONL.split(separator: "\n") {
-            let _ = damusState!.ndb.process_event("[\"EVENT\",\"subid\",\(String(noteText))]")
+            let _ = damusState!.ndb.processEvent("[\"EVENT\",\"subid\",\(String(noteText))]")
         }
     }