Add authData parameter to HTTP request functions

Introduces an optional AuthModel parameter to sendHttpRequest and streamHttpRequest, allowing authentication handling for HTTP requests. Updates all usages and tests to pass null for the new parameter where authentication is not required.

packages/better_networking/better_networking_example/lib/main.dart

@@ -109,6 +109,7 @@ class _BetterNetworkingExampleState extends State<BetterNetworkingExample> {
                 final stream = await streamHttpRequest(
                   'S1',
                   APIType.rest,
+                  null,
                   HttpRequestModel(
                     method: HTTPVerb.post,
                     url: 'http://localhost:11434/v1/chat/completions',