Expand SystemSets

[YetAnotherClown]

SystemSets, which are simply an array of systems, are currently only able to be added with Scheduler:addSystems(). This method should be expanded to allow nested SystemSets.

The idea is to allow a structure like this, where SystemSets can be used within Modules

systems/
├─ systemSet/
│  ├─ systemA.luau
│  ├─ systemB.luau
│  ├─ systemC.luau
│  ├─ init.luau

systemSet/init.luau

return {
  require("./systemA.luau"),
  require("./systemB.luau"),
  require("./systemC.luau")
}

This would be used in addition to a setup where we do not manually add our systems, but instead do:

local systems = {}

local function addSystems(instance)
    for _, child in instance:GetChildren() do
        if typeof(child) == "ModuleScript" then
            table.insert(systems, require(child))
        elseif typeof(child) == "Folder" then
            addSystems(child)
        end
    end
end

addSystems(systemsFolder)
scheduler:addSystems(systems)

By allowing us to use SystemSets like this, we can allow for users of Planck to implicitly order their systems in a SystemSet to avoid the not guaranteed order of GetChildren()