Add a small ScopedServer helper to no_proxy_test that wraps the
bind/listen/thread/cleanup dance (~13 lines per server before). Use it
to rewrite the four big tests (Redirect, BypassedTarget407, MultiHop,
KeepAlive), shaving ~100 lines.
Also drop the hardcoded port-1 / port-80 sentinels that violated the
"new standalone tests MUST use bind_to_any_port" convention and risked
collisions across gtest shards: re-use existing dynamic ports
(target.port() / bypass_server.port()) instead.
Verified pass under 4-shard parallel run.
9901a4e1f9
