[V1] API Server Performance

[robertgshaw2-neuralmagic]

SUMMARY:

• Improve API server performance by switching from AsyncStream to asyncio.Event as concurrency method between output_handler and generate() in AsyncLLM and implementing dynamic chunked streaming
• Performance looks good, but getting too bumpy ITL (we can still fall too far behind in the API server)

TODO (this PR):

• Add 3rd process to isolate detokenizer and the streaming
• Support ChatCompletions
• Support cancellation
• Better correctness testings (need to hack lm-eval to support streaming)
• Another round of performance benchmarks

[github-actions]

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