types(model): use ProjectionType for Model.hydrate()

[vkarpov15]

Fix #15437

Summary

Examples

[Copilot]

Pull Request Overview

This PR updates the type definitions for Model.hydrate() to use ProjectionType, ensuring that only the projected fields are typed accordingly.

• Adds a new test case (gh15437) in test/types/models.test.ts demonstrating the behavior of hydrating a document with a string projection.
• Verifies that projected fields are correctly typed while non-projected fields remain assignable to undefined, null, or their original type.

Comments suppressed due to low confidence (1)

test/types/models.test.ts:1034

• Consider adding a runtime check (e.g., an explicit equality assertion) to verify that 'doc1.address' is undefined when it is not projected, which can further validate the projection behavior at runtime.

expectAssignable<undefined | null | string>(doc1.address);