* test/e2e: replace RunProcesses client sleep with log-based proxy readiness detection
Replace the fixed 1500ms sleep in RunProcesses with event-driven proxy
registration detection by monitoring frpc log output for "start proxy
success" messages.
Key changes:
- Add thread-safe SafeBuffer to replace bytes.Buffer in Process, enabling
concurrent read/write of process output during execution
- Add Process.WaitForOutput() to poll process output for pattern matches
with timeout and early exit on process termination
- Add waitForClientProxyReady() that uses config.LoadClientConfig() to
extract proxy names, then waits for each proxy's success log
- For visitor-only clients (no deterministic readiness signal), fall back
to the original sleep with elapsed time deducted
* test/e2e: use shared deadline for proxy readiness and fix doc comment
- Use a single deadline in waitForClientProxyReady so total wait across
all proxies does not exceed the given timeout
- Fix WaitForOutput doc comment to accurately describe single pattern
with count semantics
* test/e2e: optimize RunFrps/RunFrpc with process exit detection
Refactor Process to track subprocess lifecycle via a done channel,
replacing direct cmd.Wait() in Stop() to avoid double-Wait races.
RunFrps/RunFrpc now use select on the done channel instead of fixed
sleeps, allowing short-lived processes (verify, startup failures) to
return immediately while preserving existing timeout behavior for
long-running daemons.
* test/e2e: guard Process against double-Start and Stop-before-Start
Add started flag to prevent double-Start panics and allow Stop to
return immediately when the process was never started. Use sync.Once
for closing the done channel as defense-in-depth against double close.
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.
