Load Base Controller Extension when autoloading

[mamhoff]

Let's use Zeitwerk to lazy load our extension.

[tvdeyen]

Thanks. A rebase with main should fix specs

[tvdeyen]

@mamhoff can this be rebased now?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.52%. Comparing base (9c6b463) to head (795c9bd).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #216   +/-   ##
=======================================
  Coverage   98.52%   98.52%           
=======================================
  Files          10       10           
  Lines         271      272    +1     
=======================================
+ Hits          267      268    +1     
  Misses          4        4           

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