Slippery Trials

This update adds new Icy-variants of Trial Spawners and Vaults. These blocks are currently functionally identical to their non-icy counterparts, they just have a slightly icy texture that is more suitable for the Frostologer castle. These blocks are not currently accessible in survival, but will be used more in future updates.

There were also some wide-ranging refactors in this update that may have broken things. These refactors should not have touched functionality, but please report any issues associated with this on Github or Discord

• Updated to run natively on Minecraft 1.21.1, 1.21 is longer compatible with Frostiful
• Added Icy Trial Spawners
• Added Icy Vaults
• Fixed Chillager Captains not dropping Ominous Bottles on death
• Refactored registrations to use static registration
• Refactored client code to use its own environment source sets