fix(serial): don't sleep forever with pending PhoneAPI output on UART consoles (#11500)

* fix(serial): don't sleep forever with pending PhoneAPI output on UART consoles

Since #11164 bounded the stream drain, a config dump can end a dispatch
with output still queued. On UART-console ESP32 boards runOnce() then
returns INT32_MAX with no RX pending, and neither rxInt() nor
onNowHasData() fires for the remaining output, so the download wedges
mid nodeinfo stream until the client happens to send a byte.

Add StreamAPI::hasPendingOutput() (transport-retained frame or queued
PhoneAPI data) and have SerialConsole::runOnce() short-poll (<=25ms)
while it holds instead of sleeping INT32_MAX. The #11164 write budget
is unchanged; idle sleep behavior with a drained queue is unchanged.
The retained-frame probe also covers the ESP32-S2 USB-CDC branch,
which takes the same INT32_MAX path.

* test(serial): restore scratch NodeDB via tearDown, trim comments to house style

A failed TEST_ASSERT longjmps out of a Unity test without running
destructors, so RAII cannot restore the swapped nodeDB pointer; install
the scratch NodeDB explicitly and restore/delete it in tearDown(),
which runs after every test outcome. Also shorten the new comments to
the two-line house limit.

src/SerialConsole.cpp

@@ -125,6 +125,10 @@ int32_t SerialConsole::runOnce()
 
     int32_t delay = runOncePart();
 #if defined(SERIAL_HAS_ON_RECEIVE) || defined(CONFIG_IDF_TARGET_ESP32S2)
+    // Nothing wakes the idle sleep for "TX space freed" or a bounded-drain remainder
+    // (#11164), so keep polling while the API holds undelivered output.
+    if (hasPendingOutput())
+        return delay < 25 ? delay : 25; // 0 continues a budget slice; else short-poll TX drain
     return Port.available() ? delay : INT32_MAX;
 #elif defined(IS_USB_SERIAL)
     return HWCDC::isPlugged() ? delay : (1000 * 20);
@@ -212,6 +216,17 @@ bool SerialConsole::finishPendingFrame()
 #endif
 }
 
+/// Report a retained USB CDC frame awaiting TX space.
+bool SerialConsole::hasRetainedFrame()
+{
+#ifdef IS_USB_SERIAL
+    concurrency::LockGuard guard(&streamLock);
+    return !frameWriter.isIdle();
+#else
+    return false;
+#endif
+}
+
 /// Protect the retained log buffer from being overwritten.
 bool SerialConsole::canEncodeLogRecord()
 {