Use BeforeConvert callback result on non-versioned updates

[JoseLion]

Closes #689

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[JoseLion]

Why did I change this?

This was the main reason for the test not catching the bug. The problem was that onBeforeConvert(..) was mutating the instance of the entity passed to the callback. This side-effect was spread through the code and reached the private method doUpdate(T entity, SqlIdentifier tableName), making the test think that it was using the value returned by the callback when it was actually using the mutated entity passed through the parameter.

I noticed that other parts of this test are already using immutability through @Value and @With, so I thought it'd make sense to use the same for Person with the minimum possible changes to preserve the behavior of the tests 🙂

[mp911de]

Thank you for your contribution. That's merged, polished, and backported now.