fix(model): throw ObjectParameterError in insertOne() if doc is not an object

[IshitaSingh0822]

What does this PR do?

Model.insertOne() did not validate that the doc argument is an object,
unlike Model.insertMany() which throws an ObjectParameterError for
non-object entries.

This PR adds the same input validation to insertOne() for consistency
and better developer experience.

Problem

When a non-object value (like a string, number, or boolean) was passed
to Model.insertOne(), Mongoose would either silently fail or throw a
cryptic internal error that was hard to debug.

Solution

Added the same ObjectParameterError check that already exists in
insertMany() to insertOne() as well.

Changes

• lib/model.js — Added ObjectParameterError check at the top of insertOne()
• test/insertOne.validation.test.js — Added 7 test cases

Why this matters

• Makes insertOne() and insertMany() behave consistently
• Gives developers a clear, actionable error message
• Zero breaking changes

Testing

All 7 new test cases pass. Existing test suite passes with no regressions.
4301 passing, 0 failing.