Vendor parse_header out of the deprecated cgi module

[Cadair]

Remove the use of the now deprecated cgi module

[codecov]

Codecov Report

Base: 90.34% // Head: 90.23% // Decreases project coverage by -0.10% ⚠️

Coverage data is based on head (8c51a76) compared to base (658a7c1).
Patch coverage: 88.46% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #112      +/-   ##
==========================================
- Coverage   90.34%   90.23%   -0.11%     
==========================================
  Files           5        5              
  Lines         611      635      +24     
==========================================
+ Hits          552      573      +21     
- Misses         59       62       +3     

Impacted Files	Coverage Δ
parfive/utils.py	90.00% <88.46%> (-0.52%)	⬇️

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