perf: optimize MessageBatch.wait_drain() to avoid asyncio.wait overhead

[gloryfromca]

Replace asyncio.wait([single_future]) with async_timeout.timeout() for better performance in high-frequency scenarios.

The original implementation using asyncio.wait() for a single future is inefficient because it creates sets and registers/removes callbacks on each call. Using async_timeout directly eliminates this overhead.

Performance improvement (tested):

• P90 latency: 479ms, 469ms -> 296ms, 299ms (~37% reduction)
• QPS: 111, 107 -> 142, 142 (~30% increase)

Changes

Fixes #

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
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[gloryfromca]

[gloryfromca]