✨ Use FlowIO instead of fcsparser

[sunnyosun]

• FlowIO only parses PnN and PnS, so we kept the previous custom code to parse all the PnX channels into .channels
• Extend CI to run on py3.9 - py3.13

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.90%. Comparing base (10e9167) to head (41b1cc9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #41      +/-   ##
==========================================
+ Coverage   89.23%   90.90%   +1.67%     
==========================================
  Files           4        4              
  Lines         130      132       +2     
==========================================
+ Hits          116      120       +4     
+ Misses         14       12       -2     

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