Fix server function warning with default features (#4453)

* fix server function warning with default features

* document and hide mock client

* fix clippy

* more clippy fixes

* fix formatting

packages/server-macro/Cargo.toml

@@ -28,6 +28,7 @@ proc-macro = true
 [features]
 axum = ["server_fn_macro/axum"]
 server = ["server_fn_macro/ssr"]
+browser = []
 reqwest = ["server_fn_macro/reqwest"]
 generic = ["server_fn_macro/generic"]