support async futex

[wokron]

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[Copilot]

Pull request overview

This PR introduces a user-space coroutine-friendly futex (condy::AsyncFutex) and adds coverage + examples demonstrating higher-level synchronization primitives (semaphore/mutex) and a producer/consumer queue built on top of it.

Changes:

• Add condy::AsyncFutex<T> awaitable synchronization primitive (include/condy/futex.hpp) and export it via include/condy.hpp.
• Add a new doctest suite covering basic wait/notify, notify-all, cross-thread notify, cancellation, and a queue scenario (tests/test_futex.cpp).
• Add a new queue example plus build/docs wiring (examples/queue.cpp, examples/CMakeLists.txt, docs/examples.md).

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/test_futex.cpp	New tests for AsyncFutex, plus queue-based integration scenario.
include/condy/futex.hpp	New condy::AsyncFutex implementation (wait/notify + cancellation).
include/condy.hpp	Exports the new futex header from the umbrella include.
examples/queue.cpp	New queue example built on AsyncFutex-based semaphore/mutex.
examples/CMakeLists.txt	Adds queue example target; fixes formatting on an existing target line.
docs/examples.md	Documents the new queue.cpp example.

Comments suppressed due to low confidence (1)

include/condy/futex.hpp:87

• request_wait_() calls detail::Context::current().runtime()->pend_work(). This makes the wait path depend on TLS context and will crash if Context::current().runtime() is null (e.g., if someone ever uses AsyncFutex outside a running Runtime, or in future refactors). Since WaitFinishHandle already stores a runtime_ (and await_suspend/register_operation already obtained a runtime), prefer using that runtime pointer (e.g., pass Runtime* into request_wait_() and use it for pend_work()).

    bool request_wait_(WaitFinishHandle *handle) noexcept {
        std::lock_guard<std::mutex> lock(mutex_);
        auto current_value = futex_.load(std::memory_order_relaxed);
        if (current_value != handle->get_old_value()) {
            return false; // No need to wait
        }
        wait_awaiters_.push_back(handle);
        detail::Context::current().runtime()->pend_work();
        return true;
    }

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[wokron]

See #99