fix(document): ensure is set to true after deleteOne()

[jagadish-555]

Summary

This PR fixes issue #15858, where Model.prototype.deleteOne() was not setting the $isDeleted property to true on the document instance after a successful deletion.

This behavior contradicted the documentation, which states that calling deleteOne() should set $isDeleted to true when the operation succeeds.

Examples

const doc = await Model.create({ name: 'test' });
await doc.deleteOne();

console.log(doc.$isDeleted()); // Now prints 'true' (used to be 'false')