feat(lazy_heap): security hardening for LazyMinHeap

- Bound constructors with MAX_CAPACITY and add fallible
  try_with_capacity / try_reserve returning LazyMinHeapError
  (CapacityTooLarge / AllocationFailed) to prevent abort on
  oversized or untrusted capacity.
- Guard stale-entry growth with an optional auto-rebuild factor
  (with_auto_rebuild / set_auto_rebuild) that runs maybe_rebuild
  after each update.
- Protect the seq counter with checked_add and renumber live
  entries on imminent u64 overflow so stale heap entries can no
  longer satisfy the (score, seq) equality check.
- Switch approx_bytes to saturating arithmetic to prevent
  overflow on pathological capacities.
- Replace derived Debug with a redacted impl that reports only
  len / heap_len / seq / auto_rebuild_factor, eliminating key and
  score disclosure via tracing::debug!, dbg!, or panic backtraces.
- Expand module docs with a Security Considerations section
  covering the above mitigations.

Made-with: Cursor

Author: TKorr