REPL: Add .clearhistory command

### What is the problem this feature will solve? This feature allows users to clear REPL history from within the REPL itself, avoiding the need to manually locate and delete the history file. Similar to how Git Bash supports `history -c`. ### What is the feature you are proposing to solve the problem? This built-in command allows users to clear REPL history from within the REPL itself, avoiding the need to manually locate and delete the history file. ### What alternatives have you considered? _No response_