Allow test runner script to increase the default width, with a minimum

[ianfixes]

Feature Request

The arduino_ci.rb test runner script hard-codes WIDTH = 80 as a target text formatting for all its checkmarks, x's, and informational outputs.

80 should definitely be the minimum, but we should explore options for letting the user decide on a larger width as per their preferences. It's unclear whether we should attempt something like tput cols (which won't work on Windows) or leave that to the user to simply collect that value on their own and apply it.

An environment variable is probably the easiest and most appropriate way to accomplish this.