[new feat sugg] Firestore / Dynamic Parallel Queries

As react query implements [dynamic parallel queries](https://react-query-v3.tanstack.com/guides/parallel-queries#dynamic-parallel-queries-with-usequeries) with _useQueries_, this library would similarly benefit from running multiple queries in parallel.

**Use case:**
Given the following structure `/parents/{parentId}/children/{childrenId}`
I want to get the first n children for parents X,Y, and possibly Z (without knowing beforehand how many parents will be queried)

**considerations**
- we don't want to use groupCollection
- in this case it's the same query, repeated multiple times, but we could have different queries