Add reply_to_address Mail extension

Action Mailbox adds `*_address`/`*_addresses` methods to `Mail::Message` for from, to, cc, and bcc, but not for reply_to. This adds the missing extension for `reply_to_address`.

Author: Mr0grog

actionmailbox/CHANGELOG.md

@@ -1,2 +1,5 @@
+*   Add `reply_to_address` extension method on `Mail::Message`.
+
+    *Mr0grog*
 
 Please check [8-0-stable](https://github.com/rails/rails/blob/8-0-stable/actionmailbox/CHANGELOG.md) for previous changes.

actionmailbox/lib/action_mailbox/mail_ext/addresses.rb

@@ -6,6 +6,10 @@ def from_address
       address_list(header[:from])&.addresses&.first
     end
 
+    def reply_to_address
+      address_list(header[:reply_to])&.addresses&.first
+    end
+
     def recipients_addresses
       to_addresses + cc_addresses + bcc_addresses + x_original_to_addresses + x_forwarded_to_addresses
     end

actionmailbox/test/unit/mail_ext/addresses_test.rb

@@ -7,6 +7,7 @@ class AddressesTest < ActiveSupport::TestCase
     setup do
       @mail = Mail.new \
         from: "[email protected]",
+        reply_to: "[email protected]",
         to: "[email protected]",
         cc: "[email protected]",
         bcc: "[email protected]",
@@ -18,6 +19,10 @@ class AddressesTest < ActiveSupport::TestCase
       assert_equal "example.com", @mail.from_address.domain
     end
 
+    test "reply to address uses address object" do
+      assert_equal "example.com", @mail.reply_to_address.domain
+    end
+
     test "recipients include everyone from to, cc, bcc, x-original-to, and x-forwarded-to" do
       assert_equal %w[ [email protected] [email protected] [email protected] [email protected] [email protected] ], @mail.recipients
     end