Fix Multiline Prompt Line Wrapping

[ColonelPanics]

Describe the change

This PR addresses an issue with multiline prompts whereby longer previous lines cause the width calculation to be incorrect, leading to strange behaviour in the terminal session. It looks like this bug was introduced in this PR.

This is the current behaviour:

https://github.com/piotrmurach/tty-reader/assets/27725639/182e74a3-6e9d-44fb-8b19-f8d2a484bf6e

With this change, the behaviour is as follows:

https://github.com/piotrmurach/tty-reader/assets/27725639/18fb9a54-ff39-43f0-8bf0-1e9992d06a26

Why are we doing this?

This change is being made because the prompt moving up the display is not desirable behaviour.

Benefits

One less bug!

Drawbacks

If any existing code was dependent on this sort of behaviour (I sure hope not!) then it will no longer work.

Requirements

• [x] Tests written & passing locally?
• [x] Code style checked?
• [x] Rebased with master branch?
• [x] Documentation updated?
• [x] Changelog updated?