ntf server implementation, updated ntf protocol, ntf client based on refactored protocol client, bare-bones SMP agent to manage ntf connections (to connect to ntf server) (#338)

* process ntf server commands

* when subscription is re-created and it was ENDed, resubscribe to SMP

* SMPClientAgent draft

* SMPClientAgent: remove double tracking of subscriptions

* subscriber frame

* PING error now throws error to restart SMPClient for more reliable re-connection (#342)

* increase TCP timeout to 5 sec

* add pragmas and vacuum db (#343)

* vacuum in each connection to enable auto-vacuum (#344)

* update protocol, token verification

* refactor SMPClient to ProtocoClient, to use with notification server protocol

* notification server client, managing notification clients in the agent

* stub for push payload

Co-authored-by: JRoberts <8711996+jr-simplex@users.noreply.github.com>

protocol/diagrams/notifications/register-token.mmd

@@ -0,0 +1,30 @@
+sequenceDiagram
+  participant M as mobile app
+  participant C as chat core
+  participant A as agent
+  participant P as push server
+  participant APN as APN
+
+  note over M, APN: get device token
+  M ->> APN: registerForRemoteNotifications()
+  APN ->> M: device token
+
+  note over M, P: register device token with push server
+  M ->> C: /_ntf register <token>
+  C ->> A: registerNtfToken(<token>)
+  A ->> P: TNEW
+  P ->> A: ID (tokenId)
+  A ->> C: registered
+  C ->> M: registered
+
+  note over M, APN: verify device token
+  P ->> APN: E2E encrypted code<br>in background<br>notification
+  APN ->> M: deliver background notification with e2ee verification token
+  M ->> C: /_ntf verify <e2ee code>
+  C ->> A: verifyNtfToken(<e2ee code>)
+  A ->> P: TVFY code
+  P ->> A: OK / ERR
+  A ->> C: verified
+  C ->> M: verified
+
+  note over M, APN: now token ID can be used