feat(auto-balance): disk in pressure

[c3y1huang]

Which issue(s) this PR fixes:

Issue longhorn/longhorn#4105

What this PR does / why we need it:

• Add a function to verify if files are the same size.
• Unit test CopyFile with sparse file.

Special notes for your reviewer:

None

Additional documentation or context

longhorn/longhorn#7576 (comment)

[derekbit]

LGTM

[codecov]

Codecov Report

Attention: Patch coverage is 80.95238% with 4 lines in your changes missing coverage. Please review.

Project coverage is 79.15%. Comparing base (3b5852c) to head (a353d42).

Files	Patch %	Lines
io/file.go	75.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #44      +/-   ##
==========================================
- Coverage   79.19%   79.15%   -0.05%     
==========================================
  Files          32       32              
  Lines        1485     1506      +21     
==========================================
+ Hits         1176     1192      +16     
- Misses        198      201       +3     
- Partials      111      113       +2     

Flag	Coverage Δ
unittests	79.15% <80.95%> (-0.05%)	⬇️

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