[PATCH v2 0/2] mul_u64_u64_div_u64: new implementation

[Nicolas Pitre]

This provides an implementation for mul_u64_u64_div_u64() that always
produces exact results.

Changes from v1 (https://lkml.org/lkml/2024/6/28/1130):

- Use the already available u128 type instead of "unsigned __int128".
- Add a test module.