add new types.wit package to hold duration

[bakkot]

Per suggestion from @lann.

[sunfishcode]

What are the advantages of having this in a dedicated interface, as opposed to just having everything that needs it just use u64 by convention?

[bakkot]

Just the usual advantages of using a type alias, I assume. Clarity, canonical interpretation, searchability, etc.

I'm not strongly attached to having this type but it already existed as monotonic-clock.duration and was used in other packages, so it seems like it would be good to have it in a more obvious place, which I assume was why @lann suggested this.

[lann]

Yes, I primarily suggested it because it is already being reused. I suppose now that I think about it, this type alias could be used as a hint for bindings generators / shared libraries to use native Duration types.

[sunfishcode]

Thanks, that sounds reasonable enough to go with here.