perf(engine): Improved DAG scheduling algorithm

[daryllimyt]

We don't just brainlessly tick and poll - instead we wait for tasks to complete to awake the scheduling coroutine.

Impact

• Removes 1s asyncio.sleep() which creates Temporal timers
• Cut tests duration by ~1.5min

[zeropath-ai]

✅ No security or compliance issues detected. Reviewed everything up to fdc7f5e.

Security Overview

• 🔎 Scanned files: 1 changed file(s)

Detected Code Changes

Change Type	Relevant files
Enhancement	► scheduler.py     Optimize task scheduling to avoid setting timers     Add pending tasks management     Improve task cleanup and cancellation

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