Move async example to asynchronous version of proc (#18078)

* improve runnableExamples in std/httpclient

* Add synchronous example.

* Update lib/pure/httpclient.nim

Co-authored-by: Timothee Cour <timothee.cour2@gmail.com>

Author: vercingetorx

lib/pure/httpclient.nim

@@ -574,15 +574,11 @@ proc newHttpClient*(userAgent = defUserAgent, maxRedirects = 5,
   ##
   ## `headers` specifies the HTTP Headers.
   runnableExamples:
-    import std/[asyncdispatch, httpclient, strutils]
+    import std/strutils
 
-    proc asyncProc(): Future[string] {.async.} =
-      var client = newAsyncHttpClient()
-      return await client.getContent("http://example.com")
-
-    let exampleHtml = waitFor asyncProc()
+    let exampleHtml = newHttpClient().getContent("http://example.com")
     assert "Example Domain" in exampleHtml
-    assert not ("Pizza" in exampleHtml)
+    assert "Pizza" notin exampleHtml
 
   new result
   result.headers = headers
@@ -616,6 +612,17 @@ proc newAsyncHttpClient*(userAgent = defUserAgent, maxRedirects = 5,
   ## connections.
   ##
   ## `headers` specifies the HTTP Headers.
+  runnableExamples:
+    import std/[asyncdispatch, strutils]
+
+    proc asyncProc(): Future[string] {.async.} =
+      let client = newAsyncHttpClient()
+      result = await client.getContent("http://example.com")
+
+    let exampleHtml = waitFor asyncProc()
+    assert "Example Domain" in exampleHtml
+    assert "Pizza" notin exampleHtml
+  
   new result
   result.headers = headers
   result.userAgent = userAgent