[LLT-6785] Report DaemonIsNotRunning instead of raw IO errors

[olekoliinyk]

Problem

nordvpnlite is-alive issued right after nordvpnlite stop fails with a raw OS error instead of DaemonIsNotRunning:
Error: Io(Os { code: 104, kind: ConnectionReset, message: "Connection reset by peer" })
Before sending a command, the CLI only checks that the daemon's socket file exists, and it reports DaemonIsNotRunning only when that check fails.
The daemon answers stop before it exits and removes the socket file, so a command landing in that window passes the check, connects, gets reset, and the IO error is propagated as-is.

Solution

Report IO errors that mean nothing is listening (refused, reset, aborted, broken pipe, EOF, not found) as DaemonIsNotRunning, same as a missing socket file.

In nat-lab: drop the sleep, return False from is_alive() instead of re-raising. Without the sleep, quit() and kill() now poll for the process to exit and the socket to disappear.

☑️ Definition of Done checklist

• Commit history is clean (requirements)
• README.md is updated
• Functionality is covered by unit or integration tests