Feature

Follow up to #5010

These just set the value of int_max_str_digits via an implementation specific command line flag (-X) and/or the environment variable. These need to be accepted in settings.rs and stored in the Settings struct. Flag::from_settings should be updated to pass the value along.

test_int_max_str_digits in test_cmd_line.py is a good place to evaluate changes, hopefully (but not necessarily) the test might will succeed after this change. You can run it locally with:

cargo run --release --features ssl,jit -- -m test -u all --slowest --fail-env-changed -v test_cmd_line`

to get some early feedback.