[Feature Request] Custom Command: Add Overload Support for Subcommands

Problem

The Custom Command API does not support overloads. Each command only allows one flat set of `mandatoryParameters` and `optionalParameters`, making it impossible to define subcommands with different parameter types under the same command name.

For example, a clan system needs:
- `/space:clan create <clanName>` → String
- `/space:clan invite <player>` → PlayerSelector

But this is currently not possible.

Workarounds (all have drawbacks)
1. Split into separate commands (`kw:clan-create`, `kw:clan-invite`) — breaks UX.
2. Use Enum + String — loses `PlayerSelector` benefits (autocomplete, validation).

Request

Add overload support to `CustomCommand`, so each overload can have its own independent parameter list — similar to how vanilla commands work.

ts
overloads: [
  { mandatoryParameters: [{ type: Enum, name: "space:create" }, { type: String, name: "clanName" }] },
  { mandatoryParameters: [{ type: Enum, name: "space:invite" }, { type: PlayerSelector, name: "target" }] }
]

This would significantly improve addon developer experience.