Add benchmark for sequential assignment.

Calculating -------------------------------------
 parallel assignment    126425 i/100ms
multi-line assignment
                        136492 i/100ms
-------------------------------------------------
 parallel assignment  6382145.2 (±10.1%) i/s -   31606250 in   5.006184s
multi-line assignment
                      9281041.8 (±11.7%) i/s -   45724820 in   5.001599s