Projectiles should pass through players

[haykam821]

Currently, projectiles collide with players, meaning they do not end up breaking any blocks.

[ShockMicro]

If we added a knockback rule, this could be intended 🤔

[haykam821]

If knockback is implemented, then projectiles passing through players could simply be dependent on the projectile not having knockback enabled. I believe the complication would be with multiple projectiles as suggested in #45.

Note that an implementation of preventing projectiles from hitting players can already be found in Shard Thief as added by NucleoidMC/Shard-Thief@50b3ec3. The event that Shard Thief uses could be moved to Stimuli so that Spleef can use it as well.