Use condition_variable for interruptible thread sleep in updateLoop

[jslauthor]

Summary

• Replace std::this_thread::sleep_for() in updateLoop() with std::condition_variable::wait_for()
• Add stop_cv.notify_one() in _deleteThread() to wake the sleeping thread immediately

This makes stop() return instantly instead of blocking for up to the full update interval (e.g. 30 seconds). Currently, _deleteThread() sets stop_thread = true and calls thread->join(), but the thread is stuck inside an uninterruptible sleep_for() and won't check the flag until the sleep finishes.

This causes GUI applications to hang for up to 30 seconds on quit when the SDK's static singleton destructor calls stop().

Changes

include/countly.hpp

• Added #include <condition_variable>
• Added std::condition_variable stop_cv member

src/countly.cpp

• updateLoop(): Replaced sleep_for with stop_cv.wait_for() using stop_thread as predicate
• _deleteThread(): Added stop_cv.notify_one() after setting stop_thread = true

Test plan

• Verified stop() returns instantly instead of blocking
• Verified update interval behavior is unchanged during normal operation (same sleep duration unless notified)
• No changes to public API

[jslauthor]

Sorry, accidentally created this. Will open again if needed!

[jslauthor]

Okay, I do need it. 😅 This lets us cancel any pending requests so the app can close cleanly. Let me know if you'd like any changes!