refactor pending_works_

[wokron]

No description provided.

[Copilot]

Pull request overview

This PR refactors how Runtime tracks pending work and determines when its event loop may exit, and adjusts Futex/Channel awaiter paths to match the new pending-work accounting.

Changes:

• Replace the “sentinel” pending_works_ behavior with an explicit exit_allowed_ flag and updated loop exit condition.
• Make pending_works_ non-atomic and restrict pend_work() / resume_work() to the current runtime thread (via assertions).
• Move pend_work() calls in Futex/Channel from request/enqueue time to the finish-handle start() path.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
include/condy/runtime.hpp	Introduces exit_allowed_, refactors exit condition, and changes pending-work tracking to non-atomic + assertion-guarded APIs.
include/condy/futex.hpp	Moves pend_work() from request_wait_() enqueue to finish-handle start().
include/condy/channel.hpp	Moves pend_work() from push/pop request enqueue paths to finish-handle start() for both push and pop.

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