actively removes stale timers

[lePereT]

What type of PR is this? (check all applicable)

• 🐛 Bug Fix
• ✅ Test

Description

Fixes retention of timer tasks when sleep.sleep_op(...) loses a choice.

Previously, sleep_op scheduled a timer task but did not cancel that task if the operation was aborted before the deadline. This meant losing timeout arms could remain in the timer heap until their deadline expired, retaining the associated suspension and captured values.

Changes:

• Add indexed heap removal support for timer entries.
• Make timer scheduling return an idempotent cancellation handle.
• Propagate cancellation handles through the scheduler and suspension APIs.
• Register the timer cancellation handle as cleanup for sleep_op.
• Add a regression test covering repeated losing sleep_op arms.

Manual test

• 👍 yes

Manual test description

Ran the relevant tests with luajit:

luajit tests/test_sleep-timer_cancel.lua
luajit tests/test_timer.lua
luajit tests/test_sleep.lua
luajit tests/test_op.lua

All passed.

Added tests?

• 👍 yes

Added to documentation?

• 🙅 no documentation needed