Fix the case of SlimefunItem#itemhandlers

[JustAHuman-xD]

Description

I found this abomination when doing reflection, this is to fix it <3

Proposed changes

• Renames the field itemhandlers in SlimefunItem to itemHandlers

Related Issues (if applicable)

N/A

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 have made sure that the proposed changes do not break compatibility across the supported Minecraft versions (1.16.* - 1.20.*).
• 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.

[github-actions]

Your Pull Request was automatically labelled as: "🧹 Chores"
Thank you for contributing to this project! ❤️

[LordIdra]

LGTM

[github-actions]

Slimefun preview build

A Slimefun preview build is available for testing!
Commit: d3e641f9

https://preview-builds.walshy.dev/download/Slimefun/4025/d3e641f9

Note: This is not a supported build and is only here for the purposes of testing.
Do not run this on a live server and do not report bugs anywhere but this PR!

[Sfiguz7]

Thank you for fixing our eyes