Move set_perms from accounts-db hardened_unpack to file_io

[kskalski]

Problem

• set_perms in hardened_unpack is calling crate::file_io::set_file_readonly for a non-unix platforms which introduces a bit weird dependency (i.e. windows-only API)
• the set_file_readonly call actually ignores the mode, which matches the way we currently call set_perms in hardened_unpack (set files as writable, I suppose for mmap functionality), but we could as well follow the passed mode
• set_file_readonly is used in both file_io and hardened_unpack, but those calls can be replaced with a call to more generic set path permissions function

Summary of Changes

• move set_perms to file_io as set_path_permissions
• remove set_file_readonly and replace calls with set_path_permissions

Note: this PR will be useful for cleaner change when extracting hardened_unpack into dedicated agave-snapshots crate (#8428)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.1%. Comparing base (c79c80f) to head (8ea87b7).

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #8439     +/-   ##
=========================================
- Coverage    83.1%    83.1%   -0.1%     
=========================================
  Files         839      839             
  Lines      367836   367847     +11     
=========================================
+ Hits       305943   305946      +3     
- Misses      61893    61901      +8     

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[brooksprumo]