Type checking of input data

[TobyBoyne]

Input data, X, is either a list object or an ndarray object. We should ensure that the handling of these objects is consistent and predictable. For example, the type hint below: encode expects a list, but we type hint this as an ndarray.

https://github.com/cog-imperial/entmoot/blob/1ae5042b83188101535f9e5c2c9047d210bc05a1/entmoot/models/enting.py#L80-L85