Allow non-integer api-level

[yujincheng08]

I would like to use upsidedown cake for the unit test. But the api-level only allows integers. How about allowing a non-integer api-level?

Hilariously, I posted this request since tiramusu #225 but nearly a year past, this is still not supported.

[ychescale9]

Thanks for raising again. Happy to review a PR :)

[yujincheng08]

@ychescale9 See #317