Optimized explosion entity exposure calculations

[RacoonDog]

Overview

This pull request comprises three optimizations:

• Optimize exposure raycasts by removing fluid handling, getting hit face, and other useless computations.
• Short-circuit exposure calculations on discarded entities.
• Remove duplicate Explosion#getExposure calls.

Since these optimizations specifically target entity-related explosion calculations, they have virtually no effect on single explosions. Chained explosions, however, see massive benefits due to the creation of dropped items & exp orbs which are then affected by the subsequent explosions.

I'm not particularly good at documentation, so suggestions are welcome.

Benchmarks

~150% improvement in time spent exploding 4096 tnts.
Benchmarked using seed -3199243952349285632 (randomly chosen) and 4096 tnt (/fill ~1 ~-7 ~ ~16 ~8 ~15 tnt)

Before:
9492 ms spent in World.createExplosion() Spark profile

After:
3832 ms spent in World.createExplosion() Spark profile

[virophagesp]

i tested this, it works well

[2No2Name]

Seems reasonable, will try to merge it soon

[virophagesp]

any updates?

[2No2Name]

I found some issues with the PR, but I am fixing them myself. No need to take action. In case you are curious:

1. Use of static fields in fast_exposure.ExplosionMixin. (This would lead to issues with switching worlds, multithreading mods, or just having two explosions in the nether and the overworld at the same coordinates)
2. Sending the wrong velocity to dead players in fast_exposure.ExplosionMixin
3. Crashing when explosion is outside the world height
4. Inspiring me to move the optimization to all raycasts, not just explosions

[2No2Name]

Rebased and included fixes / my own changes.

Thank you very much for your contribution @RacoonDog