Shellout stream execution now streams per character instead of per line

What does this Merge Request do and why?

Make Shellout .stream work with interactive terminal rewrites like when displaying a progress bar.

Previously it was waiting for a line to end (/n) now it streams characters as soon as it is available

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.