SepReader.Cols: Add JoinPathsToString (net9.0+ only due to Path.Join(Span<>) only)

[nietras]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 97.72727% with 1 line in your changes missing coverage. Please review.

Project coverage is 99.63%. Comparing base (8429e4f) to head (3d27f04).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Sep/SepReaderState.cs	97.56%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #254      +/-   ##
==========================================
- Coverage   99.65%   99.63%   -0.02%     
==========================================
  Files          54       54              
  Lines        4297     4339      +42     
  Branches      493      503      +10     
==========================================
+ Hits         4282     4323      +41     
  Misses         12       12              
- Partials        3        4       +1     

Flag	Coverage Δ
Debug	99.35% <97.72%> (-0.02%)	⬇️
Release	99.73% <100.00%> (+<0.01%)	⬆️
macos-latest	93.36% <97.72%> (+0.04%)	⬆️
ubuntu-latest	99.51% <97.72%> (-0.02%)	⬇️
windows-latest	99.51% <97.72%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.