Allow converting encoded samples if the element type matches

[ararslan]

At present, we error on convert(::Type{Samples{A}}, ::Samples{B}) for all A and B if the samples are encoded. This is reasonable since we don't want to affect how the samples get decoded. However, decoding should be based on the type of the encoded samples themselves rather than of their container; a decoder shouldn't care whether the incoming data is e.g. a full matrix or a view of a matrix. Thus we can allow conversion for encoded samples provided that only the container type is affected, not the element type.

cc @rebareh, who ran into this in some private Beacon code.

[ericphanson]

I think it should be totally fine as long as it validates (which is checked on construction by default anyway), which means the type matches the samples info (when encoded) which I think ends up the same as this explicit check.