chore: Switch to Standardrb instead of stock Rubocop

[maxveldink]

This PR

Switches from stock Rubocop to Standardrb.

• Removes rubocop and adds standard and standard-performance has dependencies
• Remove Rubocop configuration in favor of Standard configuration
• Updates Rake and CI to use Standard
• Applies Standard recommendations

Related Issues

Fixes #74

[codecov[bot]]

Codecov Report

Merging #76 (11205c3) into main (aebb755) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #76   +/-   ##
=======================================
  Coverage   98.90%   98.90%           
=======================================
  Files           6        6           
  Lines          91       91           
=======================================
  Hits           90       90           
  Misses          1        1           

Files Changed	Coverage Δ
lib/openfeature/sdk/api.rb	100.00% <100.00%> (ø)

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[josecolella]

@maxveldink: thought: Is there a benefit to moving to standardrb over rubocop?

[maxveldink]

The benefit I find with Standard is that it minimizes the number of Rubocop configuration decisions that need to be made. The ruleset they've settled on is fairly binary, and it's typically simple formatting while still getting the nice linting and performance warnings from Rubocop. Whenever I try to use stock Rubocop, I'm constantly fighting with the ruleset, or running into rules that don't apply to the specific project.

Besides that, it's a minor process change that is easy to adopt earlier in a project, which is why I proposed it now.

[maxveldink]

🙏🏻