Describe the bug
A signed int is used for the CLI buffer, which can cause the value to be negative if using backspace enough. This can lead to unintentional memory overwrites. It also deletes the '>' for the CLI.

To Reproduce
Steps to reproduce the behavior:
1.Build the smartfin_pc build
2. Run build/pc_hal/smartfin_pc
3. Enter #CLI without a trailing newline
4. Press backspace (can be multiple times)
5. See error

Expected behavior
No deletion should occur at '>' and i should not be negative.

Screenshots

Hardware Configuration(please complete the following information):

• Hardware Version [PCB revision]: Docker Build
• Potted [Y/n]: n
• Firmware Version: 94bb762