Get DayJS Version at Runtime

When inspecting objects and hitting a `dayjs` instance, its tricky to discern whether its a `dayjs` instance or something else. In `jquery` this is very easy: if the the object has a `jquery` string property thats in the format of n.n.n its a jquery instance.

In addition, I could foresee the need to detect the dayjs version at runtime.

It possible to add a property to the dayjs prototype called `dayjs` and have its value be the current version in `n.n.n` format similar to jquery?

Start by locating the dayjs prototype and the package's version source, then inspect how dayjs instances are constructed. Done means instances expose a runtime property that identifies Day.js and reports the current n.n.n version, with behavior verified by the project's existing tests.

Written by the indexing model from the issue text.