[otci] drain pending lines in OtCliCommandRunner before timing out (#13494)

In `OtCliCommandRunner.__expect_line()`, asynchronous commands loop
for `timeout` iterations, calling `self.wait(1)` in each step.
Under virtual-time simulation (`VIRTUAL_TIME=1`), `VirtualTime.go()`
advances simulation time without delay when no timer events or radio
traffic are scheduled on the node.

In each iteration, `self.wait(1)` calls `__pending_lines.get_nowait()`.
Because the background reader thread (`__otcli_reader`) transfers
output asynchronously from the subprocess stdout pipe to the queue,
a fast-forwarding simulation can exhaust all timeout iterations in
sub-millisecond wall-clock time before the reader thread has pushed
the buffered lines (such as `Done`) into `__pending_lines`. This
results in an intermittent and spurious `ExpectLineTimeoutError`.

This commit updates `__expect_line()` to drain `__pending_lines` with
a short timeout (0.1s total deadline) after the timeout loop
concludes, giving the reader thread sufficient time to process any
remaining stdout lines before raising `ExpectLineTimeoutError`.

TAG=agy
CONV=9ffc5984-d5ce-4533-ae04-87de08ed9ba7

tools/otci/otci/command_handlers.py

@@ -213,6 +213,24 @@ class OtCliCommandRunner(OTCommandHandler):
                         done = True
                         break
 
+            if not done:
+                deadline = time.monotonic() + 0.1
+                while True:
+                    remaining = deadline - time.monotonic()
+                    if remaining <= 0:
+                        break
+
+                    try:
+                        line = self.__pending_lines.get(timeout=remaining)
+                    except queue.Empty:
+                        break
+
+                    output.append(line)
+
+                    if match_line(line, expect_line):
+                        done = True
+                        break
+
             if not done:
                 raise ExpectLineTimeoutError(expect_line)