Add support for Python 3.13, update syntax to Python>=3.11, update readme

[Mark90]

Bump version to 1.9.0 with changes:

• Add support for Python 3.13
• Rewrote README.md
• Used pyupgrade to use Python 3.11 syntax
• Unpinned mypy 1.6 and updated code for mypy 1.14
  • Minor type annotation change to gather_nice_sync() and gather_sync()

Other changes:

• Update license headers and add as CI check
• Run pre-commit in CI

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.51%. Comparing base (96b7ebd) to head (dc57b4b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #42   +/-   ##
=======================================
  Coverage   80.51%   80.51%           
=======================================
  Files          13       13           
  Lines         467      467           
  Branches       62       62           
=======================================
  Hits          376      376           
  Misses         71       71           
  Partials       20       20           

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[mrijk]

LGTM