Do not infer if type has been given

[josevalim]

This is a WIP. We need to decide if we want to go ahead with this code or not. This assumes that, if the user specifies the dtype, the dtype will be taken precisely as is. We won't try to merge and fix things, which is arguably what we should do, but we need to fix the build.

To fix the build, we need to remember dtypes like {:duration, :milliseconds} must be first read as integers and then cast to the duration (perhaps this could be done directly in the Rust side).

[billylanchantin]

I think going ahead with this approach makes sense. There is a notion in Polars of the "physical" dtype:

• https://docs.pola.rs/py-polars/html/reference/series/api/polars.Series.to_physical.html

If we mirror that on the Elixir side, that may help us pass things to Rust in a safer way. Like, from_list can tell Rust that it's a list of either {:duration, _} or to_physical({:duration, _}).

IDK if that truly makes it easier or not though. I'd have to dig into our code to say more.

[josevalim]

The challenge here is that if you pass from_list([1, 2, 3], dtype: {:duration, ...}), we need to either implement this logic in the backend OR tell the user to pass dtype as integer and then they explicitly cast it to duration. Both are doable for sure.

[josevalim]

Continuing in favor of #928.