26w23b: FPS when travelling

The lag spike faced when traveling fast near the ground have been fixed/improved:

• there was a bug that happened at very high speed that triggered massive spike => this is fixed

• the Virtual Texture tech will now skip computing when the camera is moving fast to the ground. Only when the player stop the VT will catch up!

• I did a big pass on the way items are spawned/despawned when streaming terrain.

So at the end this will make traveling actually a bit faster than it was before the update.

I still have a lot of work to do if I want to do something buttery smooth, but I have some ideas on how to achieve that! Also there are a few visual glitch I need to sort out.

Thanks for playing!