Module cast

This module defines an explicit casting facility to replace Rust’s built-in as casts. The general idea is:

• Casts should be usable everywhere, including in const fns (which means we can’t use traits).
• Casts should fail to compile if a) the source or the target type changes, and b) the cast between the new pair of types would now be incorrect.
• usize is assumed to be always at least 32-bit.

Structs

• cast