When bandwidthLimitMode is "server", the work connection is wrapped by
libio.WrapReadWriteCloser with a close callback that captured the
variable being reassigned (local/rwc). At call time the callback
referenced the wrapper itself, whose closed guard was already set, so
Close returned nil without closing the underlying work connection.
For TCP proxies this left libio.Join blocked on the other copy
goroutine after the user disconnected, keeping the work connection and
the backend connection open. HTTP and UDP proxies had the same pattern.
Bind the Close method value before reassignment, and add an e2e test
verifying that the local connection is closed after the user
disconnects.
Replace the fixed 500ms sleep after each frps startup in RunProcesses
with a TCP dial-based readiness check that polls the server bind port.
This reduces the e2e suite wall time from ~97s to ~43s.
Also simplify the RunProcesses API to accept a single server template
string instead of a slice, matching how every call site uses it.