Replaces fs-err in untar_snapshot_create_shared_buffer()

[brooksprumo]

Problem

We're trying to remove the fs-err crate. For more information, please refer to #34838.

snapshot_utils::untar_snapshot_create_shared_buffer() still uses fs-err, but doesn't need to.

Summary of Changes

Replace fs-err with std::fs

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (8ff511e) 81.6% compared to head (a0b99fb) 81.6%.

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #34905     +/-   ##
=========================================
- Coverage    81.6%    81.6%   -0.1%     
=========================================
  Files         827      827             
  Lines      223884   223890      +6     
=========================================
- Hits       182841   182792     -49     
- Misses      41043    41098     +55     

[apfitzge]

lftm - curious if this function should be returning a Result<SharedBuffer> instead though?

[brooksprumo]

curious if this function should be returning a Result<SharedBuffer> instead though?

Yeah, maybe. I was surprised by the unwrap myself. That could be changed, yes. I haven't looked at the callers to see if an unwrap is impossible or not.