migrate e2e tests to pexpect

pexpect = `expect(1)` but in Python

has nice docs: https://pexpect.readthedocs.io/en/stable/

it is used to test the oil shell. source: http://www.oilshell.org/cross-ref.html?tag=pdksh#pexpect

Start by reading the pexpect documentation and the linked Oil shell pexpect usage. No repository file or test entry point is named, so first locate the existing end-to-end tests for the Go shell. Done means those tests use pexpect while preserving their current coverage and behavior.

Written by the indexing model from the issue text.