Add round-trip conversions and replace toRFC*() with init pattern

Cross-RFC Conversion Files (now with bidirectional inits):
- RFC_5321+RFC_5322.swift: RFC_5321 ↔ RFC_5322
- RFC_5321+RFC_6531.swift: RFC_5321 ↔ RFC_6531
- RFC_5322+RFC_6531.swift: RFC_5322 ↔ RFC_6531

EmailAddress Conversions:
- Replaced .toRFC5321() with RFC_5321.EmailAddress(...)
- Replaced .toRFC5322() with RFC_5322.EmailAddress(...)
- Updated EmailAddress+RFC5322.swift and EmailAddress+RFC6531.swift

Benefits:
- Cleaner init pattern: RFC_5321.EmailAddress(rfc5322)
- Round-trip conversions available for all RFC pairs
- Avoids circular dependencies between RFC packages

Author: coenttb

Sources/EmailAddress/EmailAddress+RFC5322.swift

@@ -6,7 +6,7 @@ import RFC_6531
 extension EmailAddress {
     /// Initialize from RFC5322
     public init(rfc5322: RFC_5322.EmailAddress) throws {
-        self.rfc5321 = try? rfc5322.toRFC5321()
+        self.rfc5321 = try? RFC_5321.EmailAddress(rfc5322)
         self.rfc5322 = rfc5322
         self.rfc6531 = try {
             guard

Sources/EmailAddress/EmailAddress+RFC6531.swift

@@ -6,8 +6,8 @@ import RFC_6531
 extension EmailAddress {
     /// Initialize from RFC6531
     public init(rfc6531: RFC_6531.EmailAddress) {
-        self.rfc5321 = try? rfc6531.toRFC5321()
-        self.rfc5322 = try? rfc6531.toRFC5322()
+        self.rfc5321 = try? RFC_5321.EmailAddress(rfc6531)
+        self.rfc5322 = try? RFC_5322.EmailAddress(rfc6531)
         self.rfc6531 = rfc6531
         self.displayName = rfc6531.displayName
     }

Sources/EmailAddress/RFC_5321+RFC_5322.swift

@@ -0,0 +1,37 @@
+import Foundation
+import RFC_5321
+import RFC_5322
+
+extension RFC_5321.EmailAddress {
+    /// Initialize from RFC 5322 email address
+    ///
+    /// Converts an RFC 5322 (Internet Message Format) email address to RFC 5321 (SMTP) format.
+    /// RFC 5321 has more restrictive rules than RFC 5322.
+    ///
+    /// - Parameter rfc5322: The RFC 5322 email address to convert
+    /// - Throws: If the address contains characters or patterns not allowed in RFC 5321
+    public init(_ rfc5322: RFC_5322.EmailAddress) throws {
+        try self.init(
+            displayName: rfc5322.displayName,
+            localPart: .init(rfc5322.localPart.stringValue),
+            domain: rfc5322.domain
+        )
+    }
+}
+
+extension RFC_5322.EmailAddress {
+    /// Initialize from RFC 5321 email address
+    ///
+    /// Converts an RFC 5321 (SMTP) email address to RFC 5322 (Internet Message Format).
+    /// RFC 5322 allows a superset of RFC 5321, so this conversion always succeeds.
+    ///
+    /// - Parameter rfc5321: The RFC 5321 email address to convert
+    /// - Throws: If the local part cannot be represented in RFC 5322 format
+    public init(_ rfc5321: RFC_5321.EmailAddress) throws {
+        try self.init(
+            displayName: rfc5321.displayName,
+            localPart: .init(rfc5321.localPart.stringValue),
+            domain: rfc5321.domain
+        )
+    }
+}

Sources/EmailAddress/RFC_5321+RFC_6531.swift

@@ -0,0 +1,38 @@
+import Foundation
+import RFC_1123
+import RFC_5321
+import RFC_6531
+
+extension RFC_5321.EmailAddress {
+    /// Initialize from RFC 6531 email address
+    ///
+    /// Converts an RFC 6531 (SMTPUTF8) internationalized email address to RFC 5321 (SMTP) format.
+    /// Only works for addresses that use ASCII characters only.
+    ///
+    /// - Parameter rfc6531: The RFC 6531 email address to convert
+    /// - Throws: If the address contains non-ASCII characters or patterns not allowed in RFC 5321
+    public init(_ rfc6531: RFC_6531.EmailAddress) throws {
+        try self.init(
+            displayName: rfc6531.displayName,
+            localPart: .init(rfc6531.localPart.stringValue),
+            domain: .init(rfc6531.domain.name)
+        )
+    }
+}
+
+extension RFC_6531.EmailAddress {
+    /// Initialize from RFC 5321 email address
+    ///
+    /// Converts an RFC 5321 (SMTP) email address to RFC 6531 (SMTPUTF8) format.
+    /// RFC 6531 is a superset of RFC 5321, so this conversion always succeeds.
+    ///
+    /// - Parameter rfc5321: The RFC 5321 email address to convert
+    /// - Throws: If the conversion fails
+    public init(_ rfc5321: RFC_5321.EmailAddress) throws {
+        try self.init(
+            displayName: rfc5321.displayName,
+            localPart: .init(rfc5321.localPart.stringValue),
+            domain: rfc5321.domain
+        )
+    }
+}

Sources/EmailAddress/RFC_5322+RFC_6531.swift

@@ -0,0 +1,37 @@
+import Foundation
+import RFC_5322
+import RFC_6531
+
+extension RFC_5322.EmailAddress {
+    /// Initialize from RFC 6531 email address
+    ///
+    /// Converts an RFC 6531 (SMTPUTF8) internationalized email address to RFC 5322 (Internet Message Format).
+    /// Only works for addresses that use ASCII characters only.
+    ///
+    /// - Parameter rfc6531: The RFC 6531 email address to convert
+    /// - Throws: If the address contains non-ASCII characters or patterns not allowed in RFC 5322
+    public init(_ rfc6531: RFC_6531.EmailAddress) throws {
+        try self.init(
+            displayName: rfc6531.displayName,
+            localPart: .init(rfc6531.localPart.stringValue),
+            domain: rfc6531.domain
+        )
+    }
+}
+
+extension RFC_6531.EmailAddress {
+    /// Initialize from RFC 5322 email address
+    ///
+    /// Converts an RFC 5322 (Internet Message Format) email address to RFC 6531 (SMTPUTF8) format.
+    /// RFC 6531 is a superset of RFC 5322, so this conversion always succeeds.
+    ///
+    /// - Parameter rfc5322: The RFC 5322 email address to convert
+    /// - Throws: If the conversion fails
+    public init(_ rfc5322: RFC_5322.EmailAddress) throws {
+        try self.init(
+            displayName: rfc5322.displayName,
+            localPart: .init(rfc5322.localPart.stringValue),
+            domain: rfc5322.domain
+        )
+    }
+}