Used condition variable for event polling

[datenglin]

Description

Before this change, the code uses sleep for event polling which has the drawback of potential delay of up to 0.05 seconds. This change uses threading.Condition so we can wait for the signal of scheduler having the requests.

Tests

It passed the Buildkite: https://buildkite.com/tpu-commons/tpu-inference-ci/builds/11630/steps/canvas

[github-actions]

Description

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