Fix query-result cache isolation and non-exact warm reuse

  Scope hot query-cache entries per array instead of by digest alone, so
  different arrays no longer share cached coordinates incorrectly. Preserve
  ordered query field sequence in cache keys and handle empty coordinate
  results safely.

  Restore in-memory value-path caching for arr[cond][:] now that hot-cache
  entries are array-scoped. Extend light and segment evaluators to return
  exact positions when needed so value/indices queries can populate the
  cache even when the planner does not start with exact_positions.

  Add regressions for:

  - cross-array hot-cache contamination
  - ordered cache-key collisions
  - empty cached results
  - in-memory GC cleanup of scoped hot-cache entries
  - warm cache hits for light/ultralight/medium/full value-path queries

Author: FrancescAlted