fix: add rescorer activation function for BM25

[zhengbuqian]

issue: #35853

[mergify]

@zhengbuqian E2e jenkins job failed, comment /run-cpu-e2e can trigger the job again.

[mergify]

@zhengbuqian cpp-unit-test check failed, comment rerun cpp-unit-test can trigger the job again.

[mergify]

@zhengbuqian go-sdk check failed, comment rerun go-sdk can trigger the job again.

[czs007]

/approve
/lgtm

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: czs007, zhengbuqian

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• internal/proxy/OWNERS [czs007]
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.31%. Comparing base (8275e40) to head (433e8b7).
Report is 12 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #37481   +/-   ##
=======================================
  Coverage   67.31%   67.31%           
=======================================
  Files         290      290           
  Lines       25377    25377           
=======================================
  Hits        17082    17082           
  Misses       8295     8295           

Components	Coverage Δ
Client	∅ <ø> (∅)
Core	67.31% <ø> (ø)
Go	∅ <ø> (∅)

[zhengbuqian]

rerun ut