Defer sponge command registration

[RacoonDog]

The Problem

As it currently stands, trying to register sponge commands through CommandRegistrar#EVENT from either a ClientModInitializer or a DedicatedServerModInitializer results in non-determinism as whether they are successfully registered depends on the order the initializers were invoked by fabric loader (because CommandRegistrar#EVENT is also invoked from these entrypoints).

The Solution

I added a CommandRegistrationCallback#EVENT event in the command api v1 library that is invoked before the vanilla command manager is filled with mod commands during the ServerLifecycleEvents#SERVER_STARTING callback. I then wrapped the sponge command registration event invocations in the ImplInit classes so that their registration is now deferred to the ServerLifecycleEvents#SERVER_STARTING callback rather than the mod initializers.

This pull request ensures a strict load order between sponge commands and vanilla commands without breaking backwards compatibility.

[thecatcore]

Interesting, we never realized this issue as test mod commands are registered through a ModInitialiser instead. What would be the advantage of registering them through a ClientModInitialiser or a DedicatedServerModInitialiser in this case?

[RacoonDog]

Interesting, we never realized this issue as test mod commands are registered through a ModInitialiser instead. What would be the advantage of registering them through a ClientModInitialiser or a DedicatedServerModInitialiser in this case?

In my case, I ran into this issue while I was developing https://github.com/LegacyHypixel/LegacyBetterConfig

[thecatcore]

Alright, after looking more into it, the test mods somehow don't use the command registering event. Which isn't the intended way of registering commands. Can you fix the test mods as well in this pr?