Enhancement: Allow for lazily-constructed messages

[stdedos]

https://junit.org/junit5/docs/snapshot/user-guide/#writing-tests

        assertTrue('a' < 'b', () -> "Assertion messages can be lazily evaluated -- "
                + "to avoid constructing complex messages unnecessarily.");

Maybe you can pass the library's result.getMessage() as an optional parameter (so the user can use the message themselves, or not)

Maybe a tangent to #183

[carterpage]

Are you having performance problems with the library?

[stdedos]

No, but "maybe" I could do something about #183 (comment)

I think pre-computing all tests' diffs by myself will kill performance