Fix mfd_exec()

Fixed crash due to std::env::vars() unwrap()...

Update memfd-exec fork

- Added SIGUSR1/SIGUSR2 signals to signal handler

- Changed signal handling logic
- Improved error handling and crash recovery
- Enhanced unshare logic
- Fixed process spawning and exit codes
- Various stability improvements

Fix for reuse of broken mount points

Update unshare reuse logic

- New `URUNTIME_UNSHARE` config option

- Refactored mount point reuse logic

- Added reuse of the mount point in unshare mode

Add random mount point in unshare mode

Fix print mount point path

- Updated `DwarFS` version `0.14.0` -> `0.14.1`

- Improved FUSE check
- Added logic for proper unmounting
- Added fallback handling for `fusermount` and `fusermount3` commands
- Refactoring