enhance: return topks when search in restful v2

[smellthemoon]

if nq>2, restful will flatten all the res. If one nq res has duplicate pks, the length of this slice will be less then topk. This pr
will attach topks in the output.

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[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 80.06%. Comparing base (3ab692e) to head (82f2b10).
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
...nternal/distributed/proxy/httpserver/handler_v2.go	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #39812      +/-   ##
==========================================
+ Coverage   80.04%   80.06%   +0.02%     
==========================================
  Files        1488     1488              
  Lines      205913   205913              
==========================================
+ Hits       164828   164872      +44     
+ Misses      35108    35077      -31     
+ Partials     5977     5964      -13     

Components	Coverage Δ
Client	79.24% <ø> (ø)
Core	69.40% <ø> (ø)
Go	81.78% <66.66%> (+0.02%)	⬆️

Files with missing lines	Coverage Δ
...nternal/distributed/proxy/httpserver/handler_v2.go	92.72% <66.66%> (ø)

... and 32 files with indirect coverage changes

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[smellthemoon]

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rerun go-sdk

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[tedxu]

/lgtm
/approve

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: smellthemoon, tedxu

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