feat: SelectFourMany with consolidate() for star topology

[TonySchneider]

PR Info

• Closes
• Dependencies: none
• Dependents: none

New Features

• SelectFourMany<E, F, G, H, TOP> mirroring SelectThreeMany
• SelectFour::consolidate() returning SelectFourMany
• SelectFourMany<TopologyStar>::all() returning Vec<(E::Model, Vec<F::Model>, Vec<G::Model>, Vec<H::Model>)>
• Internal consolidate_query_result_quad_star helper (mirrors consolidate_query_result_tee)

Bug Fixes

• N/A

Breaking Changes

• None - purely additive

Changes

SelectFour::all() returns flat tuples (E, Option<F>, Option<G>, Option<H>) and there's no consolidate() to roll has_many children up into Vecs the way SelectThreeMany does. Hit this fetching a parent entity along with three of its has_many children in one query - ended up batching a separate fetch for the fourth entity, which feels off given the rest of the codebase uses consolidate() consistently. This PR adds the equivalent for SelectFour, star topology only (E -> F, E -> G, E -> H); chain/tee variants can follow if needed. Reuses retain_unique_models and ModelKey so behavior matches the 3-way path. Unit tests cover single-row, sparse children, cross-product dedup, and multi-parent ordering.