fix: Prevent balancer from overloading the same QueryNode

[weiliu1031]

issue: #38718
The balancer calculates the workload of executing tasks as an ongoing score for target nodes. However, a logic issue arises when GetSegmentTaskDelta or GetChannelTaskDelta is called with collectionID=-1, which incorrectly returns zero.

Due to the incorrect global score, the executing task's workload is not properly reflected for each collection. Consequently, each collection submits its own balance task, leading to the balancer assigning excessive tasks to the same QueryNode.

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.33%. Comparing base (90de37e) to head (c99cb48).
Report is 19 commits behind head on master.

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Additional details and impacted files

@@             Coverage Diff             @@
##           master   #38719       +/-   ##
===========================================
- Coverage   81.05%   69.33%   -11.72%     
===========================================
  Files        1381      292     -1089     
  Lines      195090    26187   -168903     
===========================================
- Hits       158131    18158   -139973     
+ Misses      31398     8029    -23369     
+ Partials     5561        0     -5561     

Components	Coverage Δ
Client	∅ <ø> (∅)
Core	69.33% <ø> (ø)
Go	∅ <ø> (∅)

see 1089 files with indirect coverage changes

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