perf: add lifecycle cancellation for Activity renderLoop requestAnimationFrame

[Rohit-rk07]

Summary

Activity starts a recursive requestAnimationFrame(renderLoop) that runs for the full page lifetime, but there is no tracked RAF id/cancel path for this loop.

Code references

• js/activity.js:504 (const renderLoop = () => { ... })
• js/activity.js:514 (requestAnimationFrame(renderLoop); inside loop)
• js/activity.js:516 (initial requestAnimationFrame(renderLoop);)

Why this matters

Even with dirty-checks, the RAF callback itself still executes every frame. Without explicit lifecycle cleanup, this can:

• keep scheduling work when Activity is torn down/reinitialized,
• create duplicate loops in edge re-init flows,
• waste CPU on low-power devices.

Expected behavior

• Store RAF id (e.g. this._renderLoopRafId) when scheduling.
• Gate loop with a lifecycle flag (e.g. this._isRunning).
• Cancel RAF on teardown/destroy path (cancelAnimationFrame).

Suggested fix sketch

• Replace naked recursive calls with a managed startRenderLoop() / stopRenderLoop() pair.
• Ensure stopRenderLoop() is invoked from Activity cleanup/unload hooks.

Optional validation

• Add a unit/integration check that reinitializing Activity does not increase active RAF loop count.