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

Cargo.lock

@@ -5459,6 +5459,7 @@ dependencies = [
  "futures-channel",
  "futures-util",
  "generational-box",
+ "http 1.3.1",
  "hyper-rustls 0.27.7",
  "parking_lot",
  "pin-project",