Check for supported dtypes when adding new mag

[hotzenklotz]

Detailed Description

• Affected library: webknossos

When adding a new mag / adding data to a layer, we should assert that the data's dtype is actually supported by WEBKNOSSOS and can be rendered. If not, provide a warning.

Probably should be handled by the mag.write() method or when creating a new layer.

Supported dtypes can be found: https://docs.webknossos.org/webknossos/data_formats.html#wkw-datasets or at https://github.com/scalableminds/webknossos/issues/6581

Use Cases & Context

This could prevent user errors, e.g. uploading color layer data as uint64.