Remove upfront extension requires

This commit addresses an issue where we were requiring all extension
files upfront, which could raise errors if the required gems were not
present in the user's environment. To resolve this, we've removed the
automatic requires for ActiveRecord and ROM extensions from
lib/dry/operation.rb.

Instead, we've updated the documentation in both ActiveRecord and ROM
extension files to include the necessary require statement in the example
code. To ensure our tests continue to pass with these changes, we've also added
the requires to the spec_helper file.

See report: 92cdde9#commitcomment-146824502

lib/dry/operation.rb

@@ -3,8 +3,6 @@
 require "zeitwerk"
 require "dry/monads"
 require "dry/operation/errors"
-require "dry/operation/extensions/active_record"
-require "dry/operation/extensions/rom"
 
 module Dry
   # DSL for chaining operations that can fail

lib/dry/operation/extensions/active_record.rb

@@ -17,6 +17,8 @@ module Extensions
       # back and, as usual, the rest of the flow will be skipped.
       #
       # ```ruby
+      # require "dry/operation/extensions/active_record"
+      #
       # class MyOperation < Dry::Operation
       #   include Dry::Operation::Extensions::ActiveRecord
       #

lib/dry/operation/extensions/rom.rb

@@ -20,6 +20,8 @@ module Extensions
       # container via a `#rom` method.
       #
       # ```ruby
+      # require "dry/operation/extensions/rom"
+      #
       # class MyOperation < Dry::Operation
       #   include Dry::Operation::Extensions::ROM
       #

spec/spec_helper.rb

@@ -13,6 +13,8 @@
 Bundler.require :tools
 
 require "dry/operation"
+require "dry/operation/extensions/active_record"
+require "dry/operation/extensions/rom"
 
 SPEC_ROOT = Pathname(__dir__).realpath.freeze