[PBI] Refine subscription system on the MUI

[Minnezing]

Description & Context

Subscription system must handle the following points:

• When WebSocket is reconnected, subscriptions shall be registered again
• When new subscription is registered the system should provide a snapshot of the last update to remove render delays
  • The system should implement snapshots storage
• Remove legacy services code and replace it with unified subscription service

Acceptance Criteria

Scenario 1: WebSocket reconnection

Given WebSocket is in the RECONNECTING state
When connection is established

• Then all current subscriptions are registered again.

Scenario 2: WebSocket disconnection

Given WebSocket is in the CONNECTED state
When the connection status is changed to DISCONNECTED

• Then the system clears all current subscriptions
• Then the system notifies all listeners

Scenario 3: New subscription

When the new subscription is created

• Then the system calls its callback with snapshot data of last update (if it exists) so subscriber haven't wait for the first data

Assigned Reviewer

@jinseisieko