style(src/Foundation/Client.php): Remove redundant method declaration

- Removed redundant method declaration sendAsync
- Updated comments for clarity and consistency

src/Foundation/Client.php

@@ -62,18 +62,6 @@ public function send(Message $message): ResponseInterface
         return $this->synchronous(true)->sendAsync($message)->wait();
     }
 
-    /**
-     * @throws GuzzleException
-     */
-    public function sendAsync(Message $message): PromiseInterface
-    {
-        return $this->getHttpClient()->requestAsync(
-            $message->toHttpMethod(),
-            $message->toHttpUri(),
-            $this->normalizeHttpOptions($this->authenticator->applyToOptions($message->toHttpOptions())),
-        );
-    }
-
     /**
      * @see https://docs.guzzlephp.org/en/stable/quickstart.html#concurrent-requests
      * @see \GuzzleHttp\Pool
@@ -97,4 +85,16 @@ public function pool(iterable $messages): array
             })($messages)
         );
     }
+
+    /**
+     * @throws GuzzleException
+     */
+    public function sendAsync(Message $message): PromiseInterface
+    {
+        return $this->getHttpClient()->requestAsync(
+            $message->toHttpMethod(),
+            $message->toHttpUri(),
+            $this->normalizeHttpOptions($this->authenticator->applyToOptions($message->toHttpOptions())),
+        );
+    }
 }