Handle Unsubscription Errors and Process Accordingly

[MathNodes]

There are two messages for when and unsubscription does not work and currently it spits out the long TX Message which is unintelligible to the average user.

Here are the two known responses from failed unsubs:

The following messages should appear in respective order:

1. gRPC query timeout. Failed to broadcast message to server
2. Pending session currently on blockchain. Please try your request again later.

These response can be handled in widgets.py https://github.com/MathNodes/meile-gui/blob/c2fecdd76d7755ceef07003c8a65e3ff3b1d8d38/src/ui/widgets.py#L650

[MathNodes]

The error messages reported to the user should be in line with the above screenshots:

1. "Error connecting to gRPC server. Try your request again later."
2. "Cannot unsubscribe. Pending session still on blockchain. Try your request again later."