v2.4.0

Added

• Opt-in debug tracing for availability. A new debug?: boolean plugin option
  (default false) emits info-level reserve_debug Pino logs — one event with a stage
  field and a per-call traceId — tracing slot generation and conflict detection. Every
  silent empty-return in getAvailableSlots/checkAvailability now logs its exact reason
  and inputs; per-stage candidate counts are logged on success; the availability/slots
  endpoints and the validateConflicts write path emit request/response and conflict
  decisions; and previously-swallowed bufferFor/getExternalBusy errors surface under
  the Pino err key (still fail-open). Emits at info (not debug) so lines survive
  Pino's default production level; no output and no overhead when disabled.