Update to Minecraft 26.1

[Jikoo]

As always, please exercise caution when using development builds (assuming the CI doesn't fail, it being set to Java 21 right now).

TODO:

• Update resource pack
• Clean up messy inheritance/unnecessary Spigot-side extras
  • Spigot doesn't need extra BaseXyz classes for multi-version support yet.
  • Internal design may need some rework: composition might allow cleaner code sharing, and possibly could write a better common module for less-divergent areas like slots against the vanilla server.
• Reorganize structure?
  • Most of plugin should likely be separated from bundler aside from main class and accessor.
• Test

[Jikoo]

Looks like the problem with the build is actually the clean goal because that wipes out the freshly-compiled copy of Spigot as it no longer gets installed to the local Maven repo. I should also revisit caching for it. If I place it similarly to Paperweight's output, the default Gradle cache might just handle that.

[Jikoo]

Currently only Paper 26.1.1 and Spigot 26.1(.1) are supported and nothing has been tested. I'll get to re-adding backwards compatibility later, I'm done for the day. I fought with Gradle for a couple hours to figure out how to force it to allow dependency resolution despite "mismatching" capabilities for a while. The internal modules' inheritance is basically backwards, and I didn't know enough about Gradle or think it through far enough when I was doing the initial setup for v5.

With the advent of Mojang actually versioning things again, I will likely return to dropping old versions, particularly with versions' ages showing pretty clearly in version numbers.

I'm thinking a rolling year window for support. If anyone has strong opinions on the matter, please let me know.