Provide way to specify game seeds

[izidormatusov]

Sometimes I want to play the same game few times over. I might have a bug in my solution and want to debug it. This is much harder if the game keeps changing every single time and it is hard to trigger the weird state.

The user could provide a seed (e.g. uint64) during the start of the game and then the game would use the seed for random number generation. If the user doesn't provide seed, a random one is picked.

[jdno]

I briefly considered this when building the prototype. But right now, most of the systems run in parallel, which means the order of events is non-deterministic. Even with a shared instance of a random number generator, I'm unsure if the events are reliably ordered. I need to do more research to figure out how to do this with Bevy.

Open for suggestions if anyone has any.