duration_put::put_value truncates fractional part

[rkawulak]

For durations with a floating-point Rep type, duration_put::put_value truncates fractional part because it makes static_cast<long int>(d.count()). I guess this code will also be broken if Rep is unsigned long or larger integral type, causing an overflow.

[viboes]

While analyzing #11012 I found a solution ​https://github.com/boostorg/chrono/commit/300c0c69631de7dcc9e555bdc8ff217d9a25bb88.

Let me know if this works for you.

[rkawulak]

Seems this won't work for types narrower than int_least32_t. (And why int_least32_t in particular and not int?) I guess it would be more correct to have three SFINAE-enabled trait specialisations for all signed integral, all unsigned integral and all floating-point types, promoting them to the largest corresponding type.

[viboes]

Right, the issue I found is with int.

I don't remember if there is a constraint on the representation, but IMO, it is weird to use unsigned for duration.