Base Auto Endpoints: add context to custom serializer

The `serializer` options currently just passes in the object to transform/serialize.

```
export type Model = {
tableName: string;
schema: AnyZodObject;
primaryKeys: Array;
serializer?: (obj: object) => object;
serializerSchema?: AnyZodObject;
};
```

but I would like to access the context (mainly request params) here to decide how to transform it.

Rationale is an `expand` query param that would allow me to expand some objects in the response.

Start by locating the Model type and the serializer call sites in the Base Auto Endpoints implementation. Trace how request parameters are available, decide what context the serializer should receive, and verify that an expand query parameter can change the serialized response without breaking existing serializers.

Written by the indexing model from the issue text.