chore (client): expose a close method on the ElectricNamespace to dispose its resources

[kevin-dp]

This PR addresses the first task of #243.
As suggested, the ElectricNamespace (and thus also the ElectricClient as it extends the namespace) now exposes a close method that can be called by the user to dispose all resources used by the Electric client. This close method calls the stop on the global registry such that it also stops the client's satellite process.

[linear]

VAX-971 client: Leaky resources (Notifier subscriptions, EventEmitter listeners...)

Here I list some places in the client code which leak subscriptions to the notifier, as they are never cleared up. These are the ones we found while working on the Dart client.

• ElectricNamespace
  

  electric/clients/typescript/src/electric/namespace.ts

  Line 18 in 23e6ff1

  this.notifier.subscribeToConnectivityStateChange((notification) => {

  
  Would it make sense to have a dispose/close method in the ElectricClient class? It wouldn't close the database connection, but it would clean up internal resources used by Electric.
• Client listeners

  electric/clients/typescript/src/satellite/process.ts

  Line 342 in 1b24995

  this.client.subscribeToError(this._handleClientError.bind(this))

  
  Those listeners are not cleaned up individually nor by calling removeAllListeners on the EventEmitter.
• AuthState changes

  electric/clients/typescript/src/satellite/process.ts

  Line 188 in 23e6ff1

  this.notifier.subscribeToAuthStateChanges(handler)

  
  Possible solution: Since the subscription id is being reused, maybe there could be a dispose method in the Satellite interface.
• ConnectivityState changes

  electric/clients/typescript/src/satellite/process.ts

  Line 204 in 23e6ff1

  this.notifier.subscribeToConnectivityStateChange(

  
  Possible solution: Unsubscribe in the stop method.
• Throttle snapshot

  electric/clients/typescript/src/satellite/process.ts

  Line 151 in 23e6ff1

  this._throttledSnapshot = throttle(

  
  lodash throttle output has a method cancel.
  Possible solution: Instantiate the throttle in the start method and clean it up in stop

[balegas]

Thanks for addressing this. A couple of suggestions:

• Maybe we should have a lifecycle test for electric testing that a process is registered after the electrification and deregistered after close. I'm not sure how much code is available to test this, but if not low-hanging I'm happy to skip
• Please double check that the things that are allocated for a process are all de-allocated and that we're not leaking any resources, or not de-registering from global stuff. This might have been the last thing, but let's do another pass before closing [VAX-971] client: Leaky resources (Notifier subscriptions, EventEmitter listeners...) #243.

[balegas]

Thanks for looking into suggestions