fix(helloworld): hello-world evaluator use running avg directly

[hanxiao]

No description provided.

[github-actions]

Latency summary

Current PR yields:

• 🐢🐢 index QPS at 1664, delta to last 3 avg.: -8%
• 😶 query QPS at 28, delta to last 3 avg.: -2%

Breakdown

Version	Index QPS	Query QPS
current	1664	28
0.8.9	1749	27
0.8.8	1831	28
0.8.7	1880	30

Backed by latency-tracking. Further commits will update this comment.

[JoanFM]

I think is not a good idea to encourage to use this feature. it is impossible to reset and leads to stateful computations.

[JoanFM]

Plus this feature goes against the idea of having the ability of having a contunious Flow instance running. We have no way to reset the running average (and I think we should not have one for now)

[github-actions]

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