List limit is not applied on init and/or when encoding

[kdeme]

An SSZ List has a limit and that limit is also checked when decoding and when adding items (https://github.com/status-im/nim-ssz-serialization/blob/master/ssz_serialization/types.nim#L168) to it.

However, it is not on init from a seq nor on the encoding step. Not sure if it should and how the API should ideally look, but right now it is rather confusing.

  var theList = List[byte, 5].init(@[byte 1, 2, 3, 4, 5, 6])

  let encoded = SSZ.encode(theList) # works
  let decoded = SSZ.decode(encoded, List[byte, 5]) # Fails only at decoding