feat: add nexo support

[simondumalski]

I have created this pull request that adds Nexo support to DeluxeMenus (#155). I have tested this on my development server and have not encountered any issues. The implementation is nearly identical to the existing Oraxen hook.
Some things to note:

• The Nexo API requires Java 21, so I have had to update the target and source compatibility to that.
• The existing shadow plugin is not compatible with Java 21, so I have updated it to the shadow plugin that is being maintained by Gradle.

[iGabyTM]

We can't just bump the java version by 10 releases to add support for a plugin. This needs to be announced first.

[simondumalski]

We can't just bump the java version by 10 releases to add support for a plugin. This needs to be announced first.

Yes, this PR is more to let HelpChat know that if they want to support Nexo, they'll have to update to Java 21, as well as add the hook itself so that if anyone wants to compile it themselves, they can. Other plugins that have added Nexo support have marked their Oraxen support as Deprecated, such as CrazyCrates and HMCCosmetics.

[FaultyFunctions]

Any news on this?

[simondumalski]

I've been told a version of the Nexo API that doesn't require Java 21 is potentially being worked on. Will update this if that ever comes out.