fix: STDIN/STDOUT Integration

- Updated the DOS INT 21h handler to read from STDIN and write to STDOUT using file handles instead of directly invoking INT 16h for keyboard input.
- Replaced blocking keyboard read calls with callbacks that check the STDIN handle for data availability.
- Enhanced the handling of character input functions (AH=01h, AH=07h, AH=08h, AH=0Ah) to utilize the new STDIN/STDOUT routing.
- Removed deprecated methods for retrieving standard input and output devices from the DosFileManager.
- Added integration tests to verify that INT 21h functions correctly read from and write to the redirected STDIN and STDOUT handles.

Author: maximilien-noal