Fix //snow

[PierreSchwang]

Overview

#2976 seems to have introduced a regression - which should be fixed now

Description

• Updated #isFullBlock to actually check for the VoxelShape and not the occlusion of the block
• Updated SnowSimulator to make it more readable (hopefully?) and following Minecrafts snow / rain ticking logic closer

Submitter Checklist

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1. Make sure you are opening from a topic branch (/feature/fix/docs/ branch (right side)) and not your main branch.
2. Ensure that the pull request title represents the desired changelog entry.
3. New public fields and methods are annotated with @since TODO.
4. I read and followed the contribution guidelines.