chore!: drop parallel in favor of sequential option

[wellwelwel]

Run in parallel by default.

• --sequential is a shortcut for --concurrency=1.
• --parallel and -p options are no longer available.
• The documentation is now organized according to Poku versions.

Related:

• Version 3.0.0 (planned breaking changes and architecture improvements) #801

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.62%. Comparing base (96b8707) to head (376125b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #888      +/-   ##
==========================================
- Coverage   98.90%   98.62%   -0.28%     
==========================================
  Files          35       35              
  Lines        1820     1741      -79     
  Branches       13       15       +2     
==========================================
- Hits         1800     1717      -83     
- Misses          8       11       +3     
- Partials       12       13       +1     

Flag	Coverage Δ
linux	98.50% <100.00%> (-0.34%)	⬇️
osx	98.56% <100.00%> (-0.29%)	⬇️
windows	98.50% <100.00%> (-0.34%)	⬇️

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.