Replace time.sleep with asyncio.sleep for async calls

[MaddipatlaChetan24]

Link to Issue or Description of Change

Problem: PlaywrightComputer.current_state() and highlight_mouse() use blocking time.sleep() calls inside async methods. Since this file runs directly on the ADK agent's asyncio event loop (no thread/executor offload), each time.sleep() freezes the entire event loop — not just the current coroutine — for its duration (0.5s per screenshot, 1s per mouse highlight), stalling any other concurrent work on the loop (e.g. the agent's live session streaming).

Solution: Replace both time.sleep() calls with await asyncio.sleep(), which yields control back to the event loop instead of blocking it.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

No existing unit tests cover this file.

Manual End-to-End (E2E) Tests:
Reproduced the stall with a minimal harness: a heartbeat() coroutine ticking every 0.1s run concurrently with a coroutine calling time.sleep(1) — the heartbeat showed a full 1-second gap between ticks. Re-ran with await asyncio.sleep(1) instead — ticks stayed evenly spaced at ~0.1s with no gap. Also verified the changed file parses correctly (ast.parse).

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.