Adds a NULL-by-default lookup/populate callback seam on xce_sched_core_t,
mirroring cache_clear_cb's proven shape, so the allocation dispatch
chokepoint can consult the unsatisfiable-resreq cache without a
normal-mode-only field access in shared code. Adapters live in
alloc_cache.c and are registered only during normal-mode startup;
simulation mode leaves both callbacks NULL and always computes fresh.
Adds the scheduler-sim-live-allocation spec (requirements/design/
research/tasks) as the planning artifact this and subsequent tasks
implement against.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RLSNJhNoULvVcUhXEFafQC
