feat: implement a new system class

[iMeaNz]

Objective

Since we now have a group system, this is probably not useful anymore to store the entities inside the system for those who rely solely on the groups.
So it is probably interesting to implement a new system class without this overhead and to keep the current one for the systems that don't use the groups.

Acceptance Criteria

• 1. Implement a new system class without the entity sparse set

Dependencies

No response

Technical Details

No response

Type

Engine

[iMeaNz]

Done.
See #171 (comment) and #171 (comment) for more info

Ready for review