fix(db-mongodb): remove duplicate IDs in nested relationship queries

[ed-cscosta]

What?

When querying through a nested relationship (e.g. where: { 'movie.name': { equals: '...' } }), the $in array used to filter parent collection documents was populated with duplicate entries — each document ID was pushed twice: once as a string and once as a Types.ObjectId.

Why?

In buildSearchParams.ts, the else branch (for non-join fields) was doing:

Before:

const stringID = doc._id.toString()
$in.push(stringID)

if (Types.ObjectId.isValid(stringID)) {
  $in.push(doc._id)
}

Mongoose auto-casts 24-hex strings to ObjectId before sending queries to MongoDB, so both entries resolve to the same ObjectId. This caused every ID to appear twice in the $in array (e.g. 100 IDs → 200 entries), resulting in significantly larger queries, slower plaremnning times, and in extreme cases client disconnects due to timeouts.

How?

After:

$in.push(doc._id)

The _id returned by Mongoose's .lean() is already the correct BSON type — ObjectId for standard collections, string/number for custom ID collections — so no extra casting is needed.

A regression test was added to test/relationships/int.spec.ts that queries directors through a nested movie relationship using or conditions and asserts no duplicate documents are returned.