rpc: conn::test::complex takes a very long time (or forever) on Windows

Currently the conn::test::complex takes a very long time on my desktop and has not failed or timed out.

Here's the output from cargo test -F static-sqlite with the patches from !2756 (merged) applied to my checkout:

     Running unittests src\lib.rs (target\debug\deps\arti_rpc_client_core-9ee26cb1abe64179.exe)

running 20 tests
test conn::stream::test::unexpected_proxies ... ok
test llconn::test::reading ... ok
test msgs::request::test::preserve_fields ... ok
test msgs::response::test::response_meta_bad ... ok
test llconn::test::write_failure ... ok
test msgs::request::test::fix_requests ... ok
test msgs::request::test::parse_requests ... ok
test msgs::request::test::reencode_requests ... ok
test msgs::test::any_obj_bad ... ok
test msgs::request::test::bad_requests ... ok
test msgs::response::test::bad_json ... ok
test msgs::response::test::re_encode ... ok
test msgs::response::test::response_meta_good ... ok
test msgs::test::any_obj_good ... ok
test llconn::test::write_success ... ok
test conn::test::syntax_error ... ok
test conn::test::simple ... ok
test conn::test::arti_socket_closed ... ok
test conn::test::fatal_error ... ok
test conn::test::complex has been running for over 60 seconds