feat: add comprehensive Sorbet type annotations with ActiveSupport::Concern support

- Add sorbet-runtime dependency to gemspec
- Add comprehensive type annotations to Configuration class
- Create RBI file with mixes_in_class_methods for proper class method typing
- Add ActiveSupport::Concern shim to handle included and class_methods DSL
- Add parameter validation for edge cases when RBI bypasses runtime checks
- Update tests to expect correct error messages from manual validation
- All 26 tests passing with full type safety
- Sorbet type checker passes with no errors

This implements the ActiveSupport::Concern DSL generator approach from
https://github.com/Shopify/tapioca/pull/360 to properly handle Sorbet
type checking with ActiveSupport::Concern modules.

sorbet/rbi/shims/active_support_concern.rbi

@@ -0,0 +1,20 @@
+# typed: strict
+# frozen_string_literal: true
+
+# Shim for ActiveSupport::Concern to help Sorbet understand its DSL methods
+
+module ActiveSupport
+  module Concern
+    extend T::Sig
+
+    # Define the included method that takes a block (not the standard Module#included)
+    sig { params(block: T.proc.void).void }
+    def included(&block)
+    end
+
+    # Define the class_methods method that takes a block
+    sig { params(block: T.proc.void).void }
+    def class_methods(&block)
+    end
+  end
+end