fix(renderer-manager): make swapRenderers() actually swap renderers (#808)

[GaneshPatil7517]

hello @EdwardMoyse
The swapRenderers method only swapped local parameter references:

public swapRenderers(rendererA: WebGLRenderer, rendererB: WebGLRenderer) {
  const temp = rendererA;
  rendererA = rendererB;
  rendererB = temp;
}

Since JavaScript passes object references by value, reassigning the parameters inside the function has no effect on the caller or the class's internal state. The method silently did nothing.

Fix
Replaced the no-op local swap with logic that:

• Finds both renderers in the internal this.renderers array by index.
• Swaps their positions in the array.
• Updates mainRenderer and overlayRenderer references if either renderer is involved in the swap.
• Returns early (no-op) if either renderer is not found in the list.

Tests
Added renderer-manager.test.ts with 5 test cases covering:

• Swapping two renderers in the list
• No-op when a renderer is not in the list
• Updating mainRenderer reference when it's part of the swap
• Updating overlayRenderer reference when it's part of the swap
• Swapping a renderer with itself (identity case)