Refactor Client struct for better readability and organization

Reordered and grouped fields in the Client struct for clarity. The reorganization separates logical groups of fields, making it easier to understand and maintain the code. This includes proper grouping of TLS parameters, DSN options, and debug settings.

smtp/smtp.go

@@ -37,28 +37,45 @@ import (
 
 // A Client represents a client connection to an SMTP server.
 type Client struct {
-	// Text is the textproto.Conn used by the Client. It is exported to allow for
-	// clients to add extensions.
+	// Text is the textproto.Conn used by the Client. It is exported to allow for clients to add extensions.
 	Text *textproto.Conn
-	// keep a reference to the connection so it can be used to create a TLS
-	// connection later
+
+	// auth supported auth mechanisms
+	auth []string
+
+	// keep a reference to the connection so it can be used to create a TLS connection later
 	conn net.Conn
-	// whether the Client is using TLS
-	tls        bool
-	serverName string
-	// map of supported extensions
+
+	// debug logging is enabled
+	debug bool
+
+	// didHello indicates whether we've said HELO/EHLO
+	didHello bool
+
+	// dsnmrtype defines the mail return option in case DSN is enabled
+	dsnmrtype string
+
+	// dsnrntype defines the recipient notify option in case DSN is enabled
+	dsnrntype string
+
+	// ext is a map of supported extensions
 	ext map[string]string
-	// supported auth mechanisms
-	auth       []string
-	localName  string // the name to use in HELO/EHLO
-	didHello   bool   // whether we've said HELO/EHLO
-	helloError error  // the error from the hello
-	// debug logging
-	debug  bool       // debug logging is enabled
-	logger log.Logger // logger will be used for debug logging
-	// DSN support
-	dsnmrtype string // dsnmrtype defines the mail return option in case DSN is enabled
-	dsnrntype string // dsnrntype defines the recipient notify option in case DSN is enabled
+
+	// helloError is the error from the hello
+	helloError error
+
+	// localName is the name to use in HELO/EHLO
+	localName string // the name to use in HELO/EHLO
+
+	// logger will be used for debug logging
+	logger log.Logger
+
+	// tls indicates whether the Client is using TLS
+	tls bool
+
+	// serverName denotes the name of the server to which the application will connect. Used for
+	// identification and routing.
+	serverName string
 }
 
 // Dial returns a new [Client] connected to an SMTP server at addr.