fix(helper): threadpool to simple thread

[hanxiao]

No description provided.

[codecov]

Codecov Report

Merging #2272 (be279fc) into master (afb3ce3) will increase coverage by 1.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2272      +/-   ##
==========================================
+ Coverage   87.32%   88.39%   +1.06%     
==========================================
  Files         209      209              
  Lines       11357    11363       +6     
==========================================
+ Hits         9918    10044     +126     
+ Misses       1439     1319     -120     

Flag	Coverage Δ
daemon	51.30% <100.00%> (+0.02%)	⬆️
jina	88.69% <100.00%> (+1.11%)	⬆️

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Impacted Files	Coverage Δ
jina/helper.py	83.09% <100.00%> (+0.21%)	⬆️
jina/types/document/__init__.py	92.25% <0.00%> (+0.24%)	⬆️
jina/drivers/__init__.py	93.90% <0.00%> (+1.21%)	⬆️
jina/drivers/evaluate.py	100.00% <0.00%> (+2.81%)	⬆️
jina/drivers/segment.py	80.64% <0.00%> (+3.22%)	⬆️
jina/types/sets/chunk.py	95.83% <0.00%> (+4.16%)	⬆️
jina/executors/indexers/cache.py	100.00% <0.00%> (+4.47%)	⬆️
jina/types/sets/document.py	94.73% <0.00%> (+6.76%)	⬆️
jina/drivers/querylang/select.py	89.65% <0.00%> (+17.24%)	⬆️
jina/executors/encoders/multimodal/__init__.py	100.00% <0.00%> (+20.00%)	⬆️
... and 5 more

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[github-actions]

Latency summary

Current PR yields:

• 😶 index QPS at 938, delta to last 3 avg.: -1%
• 😶 query QPS at 13, delta to last 3 avg.: -5%

Breakdown

Version	Index QPS	Query QPS
current	938	13
1.1.0	950	13
1.0.16	944	14

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