Add Transport.isKeyExchangeRequired() to avoid unnecessary KEXINIT (#811)

* Added Transport.isKeyExchangeRequired() to avoid unnecessary KEXINIT

- Updated SSHClient.onConnect() to check isKeyExchangeRequired() before calling doKex()
- Added started timestamp in ThreadNameProvider for improved tracking

* Moved KeepAliveThread State check after authentication to avoid test timing issues

src/main/java/net/schmizz/sshj/SSHClient.java

@@ -810,7 +810,12 @@ public class SSHClient
             ThreadNameProvider.setThreadName(conn.getKeepAlive(), trans);
             keepAliveThread.start();
         }
-        doKex();
+        if (trans.isKeyExchangeRequired()) {
+            log.debug("Initiating Key Exchange for new connection");
+            doKex();
+        } else {
+            log.debug("Key Exchange already completed for new connection");
+        }
     }
 
     /**

src/main/java/net/schmizz/sshj/transport/Transport.java

@@ -71,6 +71,13 @@ public interface Transport
     void doKex()
             throws TransportException;
 
+    /**
+     * Is Key Exchange required based on current transport status
+     *
+     * @return Key Exchange required status
+     */
+    boolean isKeyExchangeRequired();
+
     /** @return the version string used by this client to identify itself to an SSH server, e.g. "SSHJ_3_0" */
     String getClientVersion();
 

src/main/java/net/schmizz/sshj/transport/TransportImpl.java

@@ -254,6 +254,16 @@ public final class TransportImpl
         kexer.startKex(true);
     }
 
+    /**
+     * Is Key Exchange required returns true when Key Exchange is not done and when Key Exchange is not ongoing
+     *
+     * @return Key Exchange required status
+     */
+    @Override
+    public boolean isKeyExchangeRequired() {
+        return !kexer.isKexDone() && !kexer.isKexOngoing();
+    }
+
     public boolean isKexDone() {
         return kexer.isKexDone();
     }