Additional uses for neural fiber

[Robotgiggle]

Stacked on #1296.

• Adds the neural staff, a cosmetic endgame variant like the quenched and mindsplice staves
• Adds neural mesh, a block that accelerates budding amethyst
  • It's a multipart block (like glow lichen) so it can be attached to multiple faces in the same blockspace
  • Each mesh attached to a budding amethyst block provides +500% growth speed (additive)
  • Covering faces does still prevent crystal growth, so the optimal number of meshes is 3 (graph)
  • It does not affect anything other than budding amethyst