fix(Blank Screen): Improve UTF-16 character handling in Typewriter class

[PriNova]

Problem

The Typewriter class, which provides the typing animation effect in chat responses, was not properly handling UTF-16 characters. This could lead to broken rendering of:

• Emoji characters 😀
• Characters outside the Basic Multilingual Plane
• Combined Unicode characters
• Other UTF-16 surrogate pairs

which resulted in a blank screen in the Cody chat.

Solution

Added proper UTF-16 character boundary handling by:

• Implementing a new getNextValidSlicePoint method that respects code point boundaries
• Using Array.from() to properly handle UTF-16 code points
• Ensuring text slicing occurs at valid character boundaries

Demo

Before fix:

Before_BlankScreen.mp4

• Shows broken emoji/special characters during typing animation

After fix:

After_BlankScreen.mp4

• Shows proper rendering of all Unicode characters without a blank screen.

Test plan

All tests were performed with the 'Temperature' setting equal to 0 (zero) to obtain deterministic results.

• Tested with various Unicode characters including:
  • Emoji sequences
  • Combined characters
  • Characters outside BMP
  • Multi-code point characters

Notes

• No breaking changes to the Typewriter interface
• Maintains existing typing animation timing and behavior
• Only affects the character boundary handling

Changelog

[jamesmcnamara]

This is nice! Thanks for contributing :)

I'd prefer if we kept the comments in place, they are helpful for new comers to the code.

If you pull the latest main, you should get this change which should fix the failing unit tests.

[PriNova]

This is nice! Thanks for contributing :)

I'd prefer if we kept the comments in place, they are helpful for new comers to the code.

If you pull the latest main, you should get this change which should fix the failing unit tests.

This was accidental because Cody deleted them, but I will add them back now.