always-on expiration doesn't persist

[slingamn]

We expire always-on clients if they're idle too long:

ergo/irc/server.go

Lines 278 to 283 in 375079e

	if checkExpiration && client.IsExpiredAlwaysOn(config) {
	// TODO save the channels list, use it for autojoin if/when they return?
	server.logger.Info("accounts", "Expiring always-on client", client.AccountName())
	client.destroy(nil)
	continue
	}

but when the server restarts, we recreate them, which seems wrong.

[slingamn]

We already have the persistent data we need to implement this because we track lastSeen! We just need to check it before creating the always-on client.

[slingamn]

Somehow I missed that we already have this? 48166b5