Fix Bug Command Hub and Support Slimefun Experimental version

[eygwi]

Description

I made this pull request because I fixed the Command Hub bug and made this plugin support the experimental version of slimefun (1.21)

Proposed changes

I changed some code in some files to adjust the slimefun experimental (1.21) and minecraft 1.21.4 api, then I also changed the command_hub.java code to fix the bug

Related Issues (if applicable)

Resolve #24

Checklist

• [ ✓] I have fully tested the proposed changes and promise that they will not break everything into chaos.
• [ ✓] I have also tested the proposed changes in combination with various popular addons and can confirm my changes do not break them.
• [✓ ] I followed the existing code standards and didn't mess up the formatting.
• [✓ ] I did my best to add documentation to any public classes or methods I added.
• I have added Nonnull and Nullable annotations to my methods to indicate their behaviour for null values
• I added sufficient Unit Tests to cover my code.

[Copilot]

Pull request overview

This PR updates the plugin to support Slimefun's experimental version (1.21) and Minecraft 1.21.4, while fixing a bug in the Command Hub inventory detection. The changes include dependency upgrades, API migrations, and code cleanup.

• Updated build configuration to use Java 21 and Paper API 1.21.4
• Migrated to Slimefun experimental-SNAPSHOT with corresponding API changes (CustomItemStack, SlimefunItems, BlockExplodeEvent)
• Fixed Command Hub bug where inventory checks used wrong Material constant (BLACK_STAINED_GLASS instead of BLACK_STAINED_GLASS_PANE)

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
pom.xml	Updated Java version to 21, migrated to Paper API 1.21.4, updated Slimefun to experimental-SNAPSHOT, updated GuizhanLib to 2.3.0, removed deprecated repositories
.vscode/settings.json	Removed IDE-specific configuration file
SupportedPluginManager.java	Removed unused Bukkit import
framed_uranium.java	Removed unused and duplicate imports (PlayerRightClickEvent, BlockUseHandler, AdvancedTech, duplicate Radioactivity)
boosted_carbonado.java	Removed unused imports (PlayerRightClickEvent, Radioactive, Radioactivity, BlockUseHandler, AdvancedTech)
FireCake.java	Removed unused imports (AdvancedTech, duplicate Radioactivity)
AdvancedSolarGenLib.java	Removed unused imports (Material, EnergyNet, command_hub)
AdvancedSolarGen.java	Removed unused import (command_hub)
handheld_digger_3.java	Removed unused imports (Material, EventHandler, Listener, PlayerItemDamageEvent)
handheld_digger_2.java	Removed unused imports (Material, EventHandler, Listener, PlayerItemDamageEvent)
ExplosiveToolBreakBlocksEvent7x7.java	Migrated from org.apache.commons.lang to lang3, removed unnecessary self-package import
ExplosiveTool7x7.java	Added ExplosionResult import, updated BlockExplodeEvent constructor for 1.21.4 API compatibility
ExplosiveToolBreakBlocksEvent4x4.java	Migrated from org.apache.commons.lang to lang3
ExplosiveTool4x4.java	Added ExplosionResult import, updated BlockExplodeEvent constructor for 1.21.4 API compatibility
ExplosiveToolBreakBlocksEvent5x5.java	Migrated from org.apache.commons.lang to lang3
ExplosiveTool5x5.java	Added ExplosionResult import, updated BlockExplodeEvent constructor for 1.21.4 API compatibility
command_hub.java	Fixed bug by changing Material.BLACK_STAINED_GLASS to BLACK_STAINED_GLASS_PANE in inventory checks; refactored event handlers with improved null safety and early returns; removed unused imports
AdvancedTech.java	Migrated CustomItemStack constructor to static create method; updated all SlimefunItems references to use .item() method

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[PranavVerma-droid]

Nice! Good Fix!