Wait for the Emacs test daemon to exit before cleanup

[conornash]

A small follow-up to #98. With that change in place, the real Emacs daemon test failed once on my machine while cleaning up its temporary directory. I've only seen it happen that one time, so the evidence is thin; the explanation below is the best I could work out, and I'm very happy to be told otherwise.

The below is the agent explanation of what this PR does:

test-emacs-tools-real-daemon failed in cleanup on macOS with DELETE-FILE-ERROR: could not delete .#outside.txt, "No such file or directory".

The test leaves an unsaved edit in the buffer visiting outside.txt, so Emacs holds a .#outside.txt lock link in the runtime directory. Cleanup sent (kill-emacs) and immediately deleted that directory, but kill-emacs returns before the daemon exits, and the daemon unlinks its lock files on the way out. The tree deletion listed the lock, the daemon removed it, and the deletion then failed on the vanished entry.

The test now records the daemon's (emacs-pid) after startup and, after (kill-emacs), waits up to 10 seconds with platform-process-alive-p for that process to exit before deleting the runtime directory.

Evidence: with an unsaved edit, the lock exists right after (kill-emacs) returns while the daemon is still alive, and is gone once the process exits. The emacs suite passes (5 cases, 70 checks) and the real-daemon test passed 10/10 consecutive runs; the race did not reproduce locally without the change, so the failing run that prompted this is the only observed occurrence.