Add Params extension with schema definition capability

Adds the basic structure for the Params extension which allows
operations to define dry-schema contracts for input validation. The extension
provides a class-level params method to define schemas, with proper
inheritance support for subclasses.

Author: aaronmallen

lib/dry/operation/extensions/params.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+begin
+  require "dry/schema"
+rescue LoadError
+  raise Dry::Operation::MissingDependencyError.new(gem: "dry-schema", extension: "Params")
+end
+
+module Dry
+  class Operation
+    module Extensions
+      # Add params validation support to operations using dry-schema
+      #
+      # When this extension is included, you can use a class-level `params` method
+      # to define a schema for validating the input to your operation's methods.
+      #
+      # @see https://dry-rb.org/gems/dry-schema/
+      module Params
+        def self.included(klass)
+          klass.extend(ClassMethods)
+        end
+
+        # Class methods added to the operation class
+        module ClassMethods
+          # Define a params schema for validating operation inputs
+          #
+          # The block is passed to `Dry::Schema.Params` to define the validation rules.
+          #
+          # @yield Block for defining the schema using dry-schema DSL
+          # @return [Dry::Schema::Params] The compiled schema
+          def params(&block)
+            @_params_schema = Dry::Schema.Params(&block)
+          end
+
+          # @api private
+          def _params_schema
+            @_params_schema
+          end
+
+          # @api private
+          def inherited(subclass)
+            super
+            if defined?(@_params_schema) && @_params_schema
+              subclass.instance_variable_set(:@_params_schema, @_params_schema)
+            end
+          end
+        end
+      end
+    end
+  end
+end