Require R 4.1.0, use shorthand lambdas

[MichaelChirico]

It's a little harder to find places where we should switch to |>, I think we can do so incrementally as we come across suitable sites.

This also drops {backports} as a dependency since we don't use it directly at this time. It can be restored if we need it later.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.24%. Comparing base (118e764) to head (143964e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2977   +/-   ##
=======================================
  Coverage   99.24%   99.24%           
=======================================
  Files         128      128           
  Lines        7291     7291           
=======================================
  Hits         7236     7236           
  Misses         55       55           

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