Allow rounding as well as truncating in `volume`

[chriscarrollsmith]

check50 cs50/problems/2024/x/volume returns failed tests if you use the round function after multiplying by the scaling factor. Rounding is arguably more correct than simply coercing the result back to an integer, which truncates the resulting number.

[guyewhite]

@yuliiazhukovetsHU Are you a pro at checks? I've actually never written one! I'd sure like to learn!

[goyalyashpal]

I think this issue can be closed per the merged request:

• issue 253 fix #265