Searchable encrypted JSON arrays: implement counted-container semantics

[tobyhede]

Searchable encrypted JSON arrays in EQL v3 need a coherent container model so
path queries, array length, and array element access agree for populated and
empty arrays.

The selected direction keeps the flat searchable-vector encoding and gives an
array container an authenticated selector for its elements. Query-time array
operations gather sibling elements through that selector instead of inferring
array shape from an entry flag.

Required behaviour

• Path queries aggregate array matches into one array result.
• Empty arrays produce an empty result and length zero without a null loop bound.
• The element selector is authenticated and included in inbound metadata
  comparison so a stored container cannot be repointed silently.
• The obsolete entry-level array marker is removed from the wire contract.
• Nested-array limitations and the resulting length, equality-partition, and
  ordering disclosure are documented explicitly.
• SQL, client, proxy, fixtures, and cross-side conformance tests land as one
  coordinated breaking change.

Sequencing

First drop STRICT from the full jsonb_path_* family —
jsonb_path_query, jsonb_path_exists, and jsonb_path_query_first — to
restore SQL function inlining, then land the array aggregation and coordinated wire changes.
Regression coverage must include
real populated and empty arrays rather than only hand-built array documents.