server: Fix idle timeout to not include connect time

When --connect-timeout and idle --timeout are both 60s, and a browser
takes ~60s to come online, it immediately got killed by the idle timeout
because `browser.lastReceived` message was set when connecting begun
and the first regular result hasn't been received yet.

Make sure to give the first test 60s from when the browser comes online.

Example before this fix:

```
$ node bin/qtap.js -b edge -r none -v --timeout 60 test/fixtures/pass.html
23:46:00 …
23:46:00 [qtap_main] get_browser edge
23:46:00 [qtap_server_S1] server_listening Serving /home/runner/work/qtap/qtap at http://localhost:37207
23:46:00 [qtap_browser_client_S1_C1_edge] browser_launch_call
23:46:00 …
23:46:00 [qtap_browser_client_S1_C1_edge] browser_spawn_command /usr/bin/microsoft-edge …
23:46:00 [qtap_server_S1] …
23:47:00 [qtap_browser_client_S1_C1_edge] WARNING browser_connect_timeout Browser did not start within 60s
23:47:00 [qtap_server_S1] browser_connect_retry Retrying, attempt 2 of 3
23:47:00 [qtap_browser_client_S1_C1_edge] browser_launch_call
23:47:00 [qtap_browser_client_S1_C1_edge] …
23:47:00 [qtap_browser_client_S1_C1_edge] browser_spawn_command /usr/bin/microsoft-edge …
23:47:00 [qtap_browser_client_S1_C1_edge] browser_connected Edge Headless connected! Serving test file.
23:47:00 [qtap_browser_client_S1_C1_edge] WARNING browser_idle_timeout Test timed out after 60s
23:47:00 [qtap_browser_client_S1_C1_edge] browser_launch_stopping BrowserStopSignal: Test timed out after 60s
23:47:00 …
23:47:00 __ERROR__
23:47:00
23:47:00 Bail out from test/fixtures/pass.html in Edge Headless:
23:47:00 Test timed out after 60s
```

Author: Krinkle

src/server.js

@@ -672,6 +672,14 @@ class ControlServer {
     // tapParser.on('plan', logger.debug.bind(logger, 'browser_tap_plan'));
 
     browser.tapParser = tapParser;
+    // It is valid for connectTimeout to be more or equal than idleTimeout.
+    // These two should be treated separately and not overlapping, as otherwise
+    // a slow launch or retried launch would eat from the first test's idleTimeout
+    // and the browser could timeout before it begins.
+    //
+    // We treat 'clientonline' as the first message received from the browser,
+    // and start counting idleTimeout only after that. .
+    browser.lastReceived = performance.now();
 
     // Optimization: The naive approach would be to clearTimeout+setTimeout on every tap line,
     // in `handleTap()` or `tapParser.on('line')`. But that adds significant overhead from