Add compatibility for the 1.20 smithing table

[iTwins]

Description

Result slot moved so need to check version for correct slot.

Proposed changes

Make result slot adapt based on minecraft version.
Also rewrote SmithingTableListener to be similar to CraftingTableListener.
SmithItemEvent and PrepareSmithingEvent exist in 1.16.

Related Issues (if applicable)

Resolves #3975

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: "✨ Fix"
Thank you for contributing to this project! ❤️

[github-actions]

Slimefun preview build

A Slimefun preview build is available for testing!
Commit: 6a4642a1

https://preview-builds.walshy.dev/download/Slimefun/3990/6a4642a1

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!

[JustAHuman-xD]

LGTM, if there was anything I missed it's probably in tests since I'm test illiterate but otherwise 👍