Document the MSVC timer resolution caveat of Tree::sleep (#1257)

Tree::sleep() waits on a std::condition_variable. On MSVC the wait_for()
timeout is rounded up to the system timer resolution (about 15.6 ms,
microsoft/STL#2173), so a 1 ms sleep can take ~16 ms and
tickWhileRunning() cannot run much faster than 64 Hz on Windows.

Add a note to the Tree::sleep() documentation, with the workaround from
the STL issue thread (timeBeginPeriod(1)) that needs no library change.

Fixes #1134

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: facontidavide

include/behaviortree_cpp/bt_factory.h

@@ -133,6 +133,11 @@ class Tree
     * @param timeout  duration of the sleep
     * @return         true if the timeout was NOT reached and the signal was received.
     *
+    * @note On MSVC, std::condition_variable::wait_for() rounds the timeout up to the
+    * system timer resolution (about 15.6 ms), see microsoft/STL#2173. A short sleep, e.g.
+    * in tickWhileRunning(), can take much longer there. Calling timeBeginPeriod(1) once
+    * at startup (Windows API, links winmm) restores a 1 ms resolution.
+    *
     * */
   bool sleep(std::chrono::system_clock::duration timeout);