[ENHANCEMENT] `splitdims` and `fusedims` to use `BlockedTuple`

[ogauthe]

As mentioned in #52 , currently splitdims uses a flat tuple of axes and check lengths to block it. We should replace this logic with a BlockedTuple of ranges.

Also linked with ITensor/TensorAlgebra.jl#22

[ogauthe]

use matricize interface instead #95