Add EntityCountDiagnosticPlugin

[waynemwashuma]

Objective

Adds a new EntityCountDiagnosticPlugin to the diagnostics module. The plugin provides a simple on-screen display of the current entity count, helping developers quickly monitor ECS entity usage during runtime.This diagnostic tool is particularly useful for:

• Identifying entity leaks (continuously increasing count)
• Performance optimization (monitoring entity population)
• Debugging spawn/despawn systems
• Understanding scene complexity in real-time

Solution

Implemented EntityCountDiagnosticPlugin, which sets up ​​​​a small black box in the top-right corner of the screen, showing the number of entities.

Showcase

Enabling the plugin in an app:

import { App, EntityCountDiagnosticPlugin } from 'wima'

const app = new App()
app.registerPlugin(new EntityCountDiagnosticPlugin())
   .run()

Migration guide

No breaking changes. The plugin is optional.

Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.