build_request_client (the client behind every JS fetch(), XHR, and ES-module
load) set no request timeout. A cross-origin XHR with a non-simple header
triggers a CORS preflight OPTIONS; if the server accepts the connection but never
answers it, op_fetch_url's send().await hung forever, the fetch promise never
settled, and the XHR was stuck at readyState 1 with no completion event ever
firing. That stranded Angular HttpClient on live.deutsche-boerse.com.
Give the client a 30s request timeout (matching the other clients in the
workspace); OBSCURA_FETCH_TIMEOUT_MS overrides it. On timeout the request errors,
op_fetch_url propagates it, and the fetch shim turns it into an XHR error/loadend,
so readyState advances to 4 and Angular's error path runs.
Verified: a server that hangs on OPTIONS now makes the XHR fire error at the
timeout (was stuck forever); a CORS-allowed cross-origin XHR still succeeds with
load/200; obstacle course 33/33.
Closes#251
SGavrl
ce67008072