rerun-fails: run all failed tests in a package at once

[dnephin]

When I first wrote --rerun-fails there were limitations with the go test -run flag that required running each test individually (https://github.com/golang/go/issues/39904). I think now that https://github.com/golang/go/commit/025308fe084264538f49924b3f52d8d6b6359658 is done (and has been in all Go versions since go1.18), this can be fixed to re-run all the tests in a package at once.