[refac] group product specific tests
[tidy] use `isinstance` iso `type(x) ==`
[tidy] use `sum` iso `reduce`
[fix] use generator expr iso `filter_type`...

Why?
[intermediate]
[impl] live decision based on number
[impl] next-state for a cell
[impl ... ] an initial next_state
[impl] count_neighbor_matrix as intermediate
[impl] solved!
[impl] count cells - broken
[test] nextstates
[impl] infinite grid by growing and shrinking
[fix] don't strip empty rows in the middle.
[tidy]
[refac] rename
[refac] rename
[refac] rename
[refac] rename
[refac] rename