feat: add access enforcement for singleton components in the systems

[iMeaNz]

Objective

We now implemented compile-time access enforcement on the various components a system can act upon.
But we are missing the singleton components.
We need to find a way to declare at startup that a system will use a singleton component, whether it is a read-only access or a write one.
Also, for less indirection, the singleton component should be cached at startup

Acceptance Criteria

• 1. Add a way for the user to declare the use of a singleton component in the system
• 2. Cache the singleton component pointer at construction (maybe using weak_ptr ?)
• 3. Make sure to enforce the access based on what is provided at construction

Dependencies

No response

Technical Details

No response

Type

Engine

[iMeaNz]

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

Ready for review