Add Let it be experiment
user
```ruby
# frozen_string_literal: true

require '../../fast/lib/fast'

# For specs using `let(:something) { create ... }` it tries to use `let_it_be` instead
Fast.experiment('RSpec/LetItBe') do
  lookup 'spec/models'
  search '(block $(send nil let (sym _)) (args) (send nil create))'
  edit { |_, (let)| replace(let.loc.selector, 'let_it_be') }
  policy { |new_file| system("bin/spring rspec --fail-fast #{new_file}") }
end.run
```
assistant