parallel_matrix_formatter: one readable display for parallel RSpec runs

Running specs with parallel_tests or parallel_split_test gives you interleaved output from every process and a separate failure report per process. parallel_matrix_formatter is an RSpec formatter that sends results from all processes over a UNIX socket to process 1, which renders a single progress display and one consolidated failure report with rerun commands. It also silences stray stdout, keeps each process’s stderr in a log, and the progress display looks like Matrix digital rain. Version...