ci: remove CARGO_FEATURES_OPTION

[cakebaker]

While looking at the "code coverage" jobs I noticed that CARGO_FEATURES_OPTION is always empty when it's used. This PR adds the missing outputs CARGO_FEATURES_OPTION to ci.yml, though I'm not sure whether CARGO_FEATURES_OPTION is even needed. This PR removes CARGO_FEATURES_OPTION and adds --all-features to where CARGO_FEATURES_OPTION was used.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.97%. Comparing base (3101aa1) to head (90bed40).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #106   +/-   ##
=======================================
  Coverage   84.97%   84.97%           
=======================================
  Files          12       12           
  Lines        5829     5829           
  Branches      475      475           
=======================================
  Hits         4953     4953           
  Misses        861      861           
  Partials       15       15           

Flag	Coverage Δ
macos_latest	84.93% <ø> (ø)
ubuntu_latest	85.17% <ø> (ø)
windows_latest	22.95% <ø> (ø)

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[oSoMoN]

We're not making use of features anyway.