Add flat, efficient, specialized (one-dimensional) array types

[Robert Smith]

Add new one-dimensional array types that are not resizable. These should be designed as a data structure used to implement other data structures (e.g., matrices, tensors, etc.) efficiently.

It's unlikely there will be a good solution that can be written in plain Coalton at present; we'll likely either need built-in compiler support, or some more expressive features of Coalton, to make this work.

Some discussion here: #931

See also a somewhat ragged implementation of polymorphic arrays here: #549