[Impl] parallel composition

[DrCatman]

requires:

• [Impl] pass through blocks #56
• [Impl] stack composition #57
• [Impl] series composition #59
• lists of blocks

[mzargham]

annotations

def parallel(blocks: List[Block])-> Block:

api

from cadcad.compose import parallel

myblock = parallel([block1, block2])

asserts

block1.domain == block2.domain

expects

myblock.domain ==  block1.domain
myblock.domain ==  block2.domain
myblock.codomain == spaces.product([block1.codomain, block2.codomain])