Type safe duration vs long to avoid unit bugs

[tobrun]

Follow up from #8576 where both @jfirebaugh as @ivovandongen suggested to look into using an object for duration instead of a long. This allows us to centralize converting logic and avoid any future unit conversion bugs due to type safety.

If we force usage of this in the public API, this would be a SemVer change. We can also opt to gradually migrate to it (leave long for public api and do a conversion to a Duration underneath until next major release).

[tobrun]

After some internal discussion, we are going to punt on using long for now. This matches the end deveoper expectations the most as Android platform code also uses long for duration.

cc @LukasPaczos