fix(laravel): preserve custom builders in model query factories

[shuvroroy]

Model instance factories returned the base Eloquent builder even when static queries used the model’s custom builder. Correct the factory methods’ instance/static distinction and preserve the custom builder and model through newQuery(), newModelQuery(), and newQueryWithoutScopes().

Existing declarations retain their signatures and source metadata; explicit return types that select another builder or model remain authoritative. Return-type transformations use the existing interning cache.

Adds regression coverage for generic and non-generic builders, inherited configuration, explicit overrides, completion, and runtime behavior. Removes completed L55 from the backlog.

Stack: depends on #447. This stacked PR targets upstream main, so its diff includes the unmerged dependency. The L55 change is commit 7d608a7e; merge the dependency first.

Validation: full cargo test, both required clippy runs, cargo fmt --check, PHP syntax/runtime assertions, and Laravel analysis with exactly its three intentional diagnostics.

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