Scheduler.deinit closes the bounded leaks B1 documented: it reaps any leftover
ready fibers, frees every heap Task from go (now tracked via a task_allocs
field), frees the timers/io_waiters/task_allocs List backings, and closes the
lazily-opened kqueue fd. Terminal + idempotent; the per-spawn/go closure env
remains unfreeable (language limitation). Locked by
examples/concurrency/1820-concurrency-fiber-scheduler-deinit.sx, which exercises
every freed resource under a tracking GPA (freed by deinit: 5, kq reset to -1).
Also converts plain-struct '= ---'+field-assign init to '.{ ... }' literal init
where '---' carries no meaning: Scheduler.init, Dock.make, and the fiber
examples 1811/1813/1814/1816 (partial literals zero-fill the index-filled array
fields). Unions, '---'-feature tests, the 0154 regression, documented
generic-pack gaps, and loop/conditional inits are intentionally left on '---'.
Add a virtual clock + sleep timers to the M:1 scheduler so fibers
schedule in reproducible simulated time. Scheduler gains clock_ms (the
virtual clock, advances only as timers fire), a timers list, now_ms(),
sleep(ms) (arm {clock_ms+ms, current} + suspend), and a timer-driven
run (drain ready -> fire earliest timer -> advance clock -> wake ->
repeat; the orphan-suspend deadlock check is preserved for a genuine
no-timer park). Wakes fire in deadline order with a FIFO tiebreak.
Adversarial review found a use-after-free: a fiber woken early (manual
or Task wake) before its sleep timer fired was reaped while its Timer
kept a dangling *Fiber, so a later fire dereferenced freed memory.
Fixed: wake evicts the fiber's pending timer (cancel_timer_for) -- every
re-ready path funnels through wake, so no stale timer outlives its fiber.
Examples: 1814 (sim-timer deadline ordering), 1815 (early-wake timer
eviction regression). Suite green 753/0.
