Add Codable to RFC_5322.Message and CustomStringConvertible to LocalPart

Protocol conformance improvements:
- RFC_5322.Message: Add Codable for full message serialization
- RFC_5322.EmailAddress.LocalPart: Add CustomStringConvertible for debugging

Enables JSON/plist serialization of complete RFC 5322 messages and
improves debugging output for local parts.

Author: coenttb

Sources/RFC_5322/RFC 5322 Message.swift

@@ -32,7 +32,7 @@ extension RFC_5322 {
     ///
     /// let emlContent = message.render()
     /// ```
-    public struct Message: Hashable, Sendable {
+    public struct Message: Hashable, Sendable, Codable {
         /// Originator - From field
         public let from: EmailAddress
 

Sources/RFC_5322/RFC 5322.swift

@@ -107,7 +107,7 @@ extension RFC_5322 {
 // MARK: - Local Part
 extension RFC_5322.EmailAddress {
     /// RFC 5322 compliant local-part
-    public struct LocalPart: Hashable, Sendable {
+    public struct LocalPart: Hashable, Sendable, CustomStringConvertible {
         private let storage: Storage
 
         /// Initialize with a string
@@ -150,6 +150,9 @@ extension RFC_5322.EmailAddress {
             }
         }
 
+        /// Description for CustomStringConvertible
+        public var description: String { stringValue }
+
         // swiftlint:disable:next nesting
         private enum Storage: Hashable {
             case dotAtom(String)  // Regular unquoted format