Delay checking upstream version information

[GetPsyched]

This code was introduced in v0.5.1: https://github.com/CharaChorder/nexus/blob/3e6d11fa2721219835556ec1eb2e5e7f1898e100/nexus/__main__.py#L174-L175 The problem here is that this delays the launch of the application.

Probably 2 ways of solving this:

1. Only run this function if it hasn't been run in the last 24 hours
2. Lazy load the check so that the application can launch normally and the version can be checked in the background