fix: Unsafe shell command constructed from library input

[opsysdebug]

Fix this problem, we should avoid passing interpolated strings to system that are constructed from potentially untrusted input. Instead, we should use the form of system that takes each argument separately, which bypasses the shell and avoids interpretation of special characters. In this case, we can replace system "command -v #{tool} > /dev/null" with system("command", "-v", tool, out: File::NULL, err: File::NULL). This approach ensures that the tool argument is passed directly to the command without shell interpretation, and the output is redirected to /dev/null in a safe, cross-platform way. We only need to change the implementation of tool_exists? in lib/install/helpers.rb.