http: every completed http.get leaves a socket open (fd leak → ECONNREFUSED after ~1,015 requests); server keeps a socket per curl connection #11452

Found by the tokio-removal measurement (#11451) on main bd8936e98e.

Every completed in-process http.get round trip leaves one socket open. After 300 requests there are 301 open fds; BEFORE (d8f24f15ed) had 6. At the default 1024 open-file limit, the program then fails with connect ECONNREFUSED after about 1,015 sequential requests. Node and the BEFORE build complete 2,000.

Separately, in both arms the http server keeps one socket per accepted connection when hit by curl (206 open after 200 requests). The keep-alive load test doesn't trigger this.

Likely suspects:

• the client side, since perry-ext-http: node:http/https client on turnloop only; drop reqwest + tokio-rustls (tokio lane C) #11205 moved the http client onto turnloop, possibly the keep-alive agent pool not releasing sockets that are not reused;
• the server side not closing its socket on Connection: close or at EOF.

Repro and fd counts are in benchmarks/tokio-removal/ in #11451. This is a production-impacting leak for any long-running program making outbound http requests.