PostState.ensurePostWakeup

void ensurePostWakeup(Slot,  AllocFn,  CheckFn,  UpdateFdsFn,  SetCbFn)(
          scope  Slot[]  slots,
          scope  AllocFn allocToken,
          scope  CheckFn checkLimit,
          scope  UpdateFdsFn updateFds,
          scope  SetCbFn setCallback,
          ref  ulong  registrationSeq,
          ref  size_t watcherCount,
          size_t maxWatchers,
          size_t openFds,
          size_t maxFds)

@trusted nothrow

Lazily create the post wakeup handle and register a watcher slot.

Allocates a mutex, creates a wakeup handle, checks resource limits, allocates a watcher token, and fills the slot. The caller provides callbacks for platform-specific operations (token allocation, limit checking, fd tracking).

Parameters

`slots`	Watcher slot array.
`allocToken`	Callback: `() => Token` to allocate a token.
`checkLimit`	Callback: `(LimitKind, size_t current, size_t limit) => bool`.
`openFds`	Callback: `() => size_t` for current FD count.
`maxWatchers`	Maximum watcher limit.
`maxFds`	Maximum FD limit.
`updateFds`	Callback: `(long delta) => void`.
`setCallback`	Callback: `(ref Slot) => void` to set the wakeup callback.
`registrationSeq`	Reference to registration sequence counter.
`watcherCount`	Reference to watcher count.