fix: cleanup cache expire skip staging

[sjp00556]

disk cache cleanup expire cache items should skip staging cache items which size is <0, otherwise it will add wrong cache.used

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 56.03%. Comparing base (83b2ba2) to head (86681e5).

Files	Patch %	Lines
pkg/chunk/disk_cache.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4434      +/-   ##
==========================================
+ Coverage   56.01%   56.03%   +0.01%     
==========================================
  Files         154      154              
  Lines       40134    40136       +2     
==========================================
+ Hits        22483    22492       +9     
+ Misses      15133    15128       -5     
+ Partials     2518     2516       -2     

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