Support the HQL JOIN pattern over an embedded array via UNNEST, translating it to MongoDB's $unwind + $match pipeline.

Example HQL:

SELECT c, li FROM Cart c JOIN LATERAL UNNEST(c.lineItems) li WHERE li.sku = 'WIDGET-1' AND li.qty > 2

Expected MQL:

[
  { "$unwind": "$lineItems" },
  { "$match": { "lineItems.sku": "WIDGET-1", "lineItems.qty": { "$gt": 2 } } }
]

This shape multiplies rows: one result row per matching lineItem, exactly like a relational join. Unlike the EXISTS shape (which maps to $elemMatch and preserves parent cardinality), this requires $unwind to materialize each array element as a separate document.