Array property with object items not loaded correctly

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## Steps to reproduce

Define a model with an array property, where the item type contains a buffer.

```ts
@model()
export class DemoModel extends Entity {
@property.array(Item)
items: Item[];
}

@model()
export class Item extends Model {
@property()
buffer: Buffer;
}
```

Store and load an instance of this model.

```ts
await this.demoModelRepository.create({items: [{buffer: Buffer.from('data')}]});
const demo = await this.demoModelRepository.findOne();
console.log(demo?.items[0].buffer.toString())
```

## Current Behavior

Prints nothing. The buffer in the loaded object is empty.

## Expected Behavior

Prints "data".

## Link to reproduction sandbox

https://github.com/leanil/array-prop-bug
(Just `npm start` it, the observer performs the test on start.)

## Additional information

linux x64 16.17.0

├── @loopback/boot@5.0.9
├── @loopback/core@4.0.9
├── @loopback/repository@5.1.4
├── @loopback/rest-explorer@5.0.9
├── @loopback/rest@12.0.9
├── @loopback/service-proxy@5.0.9
├── loopback-connector-mongodb@6.2.0

Behaves the same way with `7.0.0-alpha.1`.
The absence of an array case around [here](https://github.com/loopbackio/loopback-connector-mongodb/blob/master/lib/mongodb.js#L444-L467) seems suspicious to me.

Start by running the linked reproduction with `npm start` and inspect `lib/mongodb.js` around lines 444-467, where the issue reports that array handling may be missing. Trace how the nested Item buffer is loaded and verify completion when the reproduction prints `data` instead of an empty value.

Written by the indexing model from the issue text.