Add Minecraft 1.20.4 compatibility

[keilogic]

Summary

• build against Paper 1.20.4 and Java 17 with plugin api-version 1.20
• replace Java 21-only collection helpers and Math.clamp calls with Java 17-compatible code
• add compatibility helpers for the newer item glint API and renamed particle constants
• update FoliaLib to its published com.tcoded coordinate so Maven can resolve it

Closes #41.

Validation

• mvn -q -DskipTests package using Java 17
• git diff --check
• verified the built jar is Java 17 bytecode and contains api-version: '1.20'