Knit row stitch check

Check a knitting pattern row by row to make sure every row can actually be worked with the stitches on the needle.

A knitter casts on cast_on stitches. Each row of the pattern is a string of instructions separated by single spaces, worked left to right across all the stitches currently on the needle. Every instruction uses up some stitches from the needle and produces some new ones:

A group (instr instr ...)xN means the instructions inside the brackets are worked N times in a row; groups are never nested. For example (k2tog yo)x2 is the same as k2tog yo k2tog yo.

A row is valid when the total number of stitches its instructions use equals the number of stitches on the needle at the start of that row. The stitches it makes are then on the needle for the next row. Stop at the first invalid row: it and every later row are not worked.

Input: cast_on, the starting stitch count, and rows, the list of row strings.

Output: a list with the stitch count on the needle after each valid row, in order, ending just before the first invalid row (or after the last row if all are valid). Return [] if rows is empty or the first row is invalid.