* Revert "Revert Option<Child> process handling"
This reverts commit 2af30086858d104dcb0ec87383996c36bcaa7371.
* Add a set of failure regexes to test command output
* Allow debug-printing TestChild again
* When the child is dropped, check any remaining output
* Document a wait_with_output edge case
* Improve failure regex panic output
* Improve builder ergonomics
* Add internal tests for failure regex panics
It would be easy to disable these panics, and never realise.
* Add some module structure TODOs
* Stop panicking if the child process has already been taken
* Add test APIs for consuming child output lines
* Fix a hang on child process drop
* Handle output being already taken in wait_with_output
And document some edge cases we don't handle yet
* Use bash's read command in the TestChild stderr test
And check the actual command we're using to see if it errors.
* Pretty print full failure regex list
* Add the test child command line to the failure regex logs