Remove mergify config

[benjeffery]

Migration to GitHub merge queue

This PR removes the .mergify.yml configuration file as part of migrating from Mergify to GitHub's native merge queue functionality.

The branch protection rules have been updated to include the required status checks, and merge queue has been enabled on the main branch.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.23%. Comparing base (dc7a7e6) to head (b8657f2).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2409   +/-   ##
=======================================
  Coverage   91.23%   91.23%           
=======================================
  Files          20       20           
  Lines       11828    11828           
  Branches     2295     2295           
=======================================
  Hits        10791    10791           
  Misses        568      568           
  Partials      469      469           

Flag	Coverage Δ
C	91.23% <ø> (ø)
python	98.68% <ø> (ø)

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