Function acquire_lock 

pub fn acquire_lock() -> Result<LockGuard, Error>

Acquires a system-wide lock to prevent concurrent modifications to the Zoi store.

Locking Mechanism:

• Attempts to open/create ~/.zoi/pkgs/lock.
• Uses flock (via fs2) to acquire an exclusive advisory lock on the file.
• If busy, reads the file to display the PID of the process currently holding the lock.
• Once acquired, writes the current process PID to the lock file.

This ensures that operations like install, uninstall, and update never run simultaneously, preventing database and filesystem corruption.

Errors

Returns an error if the lock cannot be acquired or if file operations fail.