file url fixes

[valtron]

Uses Path.as_uri to create file URIs from in all the places that I found.

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 81.05%. Comparing base (1589489) to head (ff8c704). :warning: Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9171      +/-   ##
==========================================
+ Coverage   81.03%   81.05%   +0.02%     
==========================================
  Files          77       77              
  Lines       13627    13625       -2     
  Branches     2039     2038       -1     
==========================================
+ Hits        11042    11044       +2     
+ Misses       1912     1909       -3     
+ Partials      673      672       -1     

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[ThomasWaldmann]

Thanks! I cherry-picked your commit into my PR branch where windows CI is enabled:

https://github.com/borgbackup/borg/actions/runs/19363117646/job/55399592469?pr=9170

It's better, but still some path/URL related failures.

BTW, I also did some other Windows-related changes there, have a look please...