[Pre-RFC] `cargo package` should include fewer files by default

newpavlov:

to be able to execute tests on no_std targets (with some minor tweaking).

This is a strong reason to use include_bytes!(). But most projects do not support running tests outside the host environment at all. I’m not saying that include_bytes!() should always be avoided; rather, that it has significant disadvantages and should be used thoughtfully rather than for all test data.