fix: Error when using with when the child references a parent but not using the parent's id column, but rather another column that is a unique index.

[joc-a]

• When a column in a child table references a column in the parent table that is not of type EntityID, a "is not in record set" error occurs because entities.groupBy { it.readValues[parentTable.id] } should be entities.groupBy { it.readValues[refColumn] } instead.
• After that was fixed, when we loop over the entities grouped by refColumn, we attempt to store the referenced column value in the cache, which does not compile because it's not the right type expected by cache.getOrPutReferrers, so we need to find the parent entity that matches the value of the refColumn and use its entityId to store it in the cache.
• The last step was to fix the invocation of findById, which was being invoked on this, which is the child entity, using id as EntityID<ID> which is for the parent entity. The fix is to find the child entity by using refColumn, which is the column in the child table that references the id in the parent table.