Account Tracker Controller subscribe MultichainNetworkController:didChange

At AccountTrackerController we do save the newly added chain IDs in the accountsByChainId, but through a pooling mechanism in mobile, or an event in Engine.

We should add a subscription in the AccountsTrackerController instead to immediately add the chainId (I think even with 0 balance), so we don't have that state out of sync for briefs moments.

The reason for this is because when we add a newly network on ramps and switch to it, since the balance was not there, we were seeing a crash: https://github.com/MetaMask/metamask-mobile/pull/13307#discussion_r1964184480

The thoughts if this is a viable solution for this issue are highly appreciated!

Start by tracing AccountTrackerController/AccountsTrackerController and the MultichainNetworkController:didChange entry point, then compare the mobile pooling mechanism with the Engine event path. Done means newly added chain IDs appear immediately in accountsByChainId, including zero-balance chains, without the reported switch-to-new-network crash.

Written by the indexing model from the issue text.