archive: preserve pre-open original atime, fixes #6194

[ThomasWaldmann]

When creating an archive with --atime on platforms without O_NOATIME, opening a file for reading could update atime before we recorded it (thus we archived the updated atime, not the original one).

Capture pre-open path-based-stat atime and use it
if it pre-dates the atime we got from the fd AND
if it refers to same fs object (avoid race condition).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.62%. Comparing base (a25856a) to head (f7dc254).
⚠️ Report is 1 commits behind head on 1.4-maint.

Additional details and impacted files

@@              Coverage Diff              @@
##           1.4-maint    #9181      +/-   ##
=============================================
+ Coverage      80.59%   80.62%   +0.02%     
=============================================
  Files             38       38              
  Lines          11251    11255       +4     
  Branches        1769     1770       +1     
=============================================
+ Hits            9068     9074       +6     
+ Misses          1614     1613       -1     
+ Partials         569      568       -1     

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[ThomasWaldmann]

Strange: test_atime still fails on cygwin.