Add system group support to scheduler configuration

[waynemwashuma]

Objective

Introduce system group support to the scheduling configuration layer.

• Add system group registration to SchedulerBuilder
• Extend SystemConfig with optional group metadata
• Prepare the scheduler architecture for grouped system organization and execution

Solution

Previously, systems could only be registered as a flat list within the scheduler builder.

This limited the ability to:

• Organize systems into logical execution groups
• Attach metadata to groups
• Build future grouped execution or ordering behavior

Why this approach

Adding grouping metadata at the configuration layer:

• Keeps the scheduler extensible

• Avoids coupling group semantics directly into system execution

• Enables future features such as:

  • grouped ordering
  • conditional execution
  • hierarchical scheduling
  • debugging/visualization tooling

Using constructor labels also aligns with the engine's existing type-based identification patterns.

Showcase

Before

Systems were registered independently,No grouping metadata existed.:

new SystemConfig(system, 'update')

After

Systems can now declare a group:

new SystemConfig(system, 'update', RenderSystems)

Groups can also be registered explicitly:

builder.addGroup({
  label: RenderSystems
})

Benefits:

• Systems can now be categorized structurally and semantically
• Scheduler configuration becomes more extensible
• Future grouped execution logic can build on existing metadata

Notes:

• System grouping currently introduces configuration metadata only
• Existing scheduling behavior remains unchanged
• System groups is optional and fully backwards compatible

Migration guide

No migration required.

Checklist

• I have updated the documentation accordingly.
• I have added tests to cover my changes.