Added unit tests for the scheduler cache snapshot functionality

[anujagrawal699]

Description:
This PR adds comprehensive unit tests for the scheduler cache snapshot functionality. This improves code coverage and ensures reliable behavior of this critical scheduling component.

Additions:

1. pkg/util/lifted/scheduler/cache/snapshot_test.go

Test Coverage:

1. pkg/util/lifted/scheduler/cache/snapshot_test.go : 0% to 100%

What type of PR is this?
/kind feature

Which issue(s) this PR fixes:
Fixes a part of #5470

Does this PR introduce a user-facing change?:

NONE

[karmada-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 42.15%. Comparing base (057cf86) to head (8ea31a8).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5770      +/-   ##
==========================================
- Coverage   42.31%   42.15%   -0.16%     
==========================================
  Files         655      655              
  Lines       55756    55756              
==========================================
- Hits        23591    23503      -88     
- Misses      30651    30765     +114     
+ Partials     1514     1488      -26     

Flag	Coverage Δ
unittests	42.15% <ø> (-0.16%)	⬇️

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