Fix IRC listener relay of bodies and modes, and JOIN names (closes #127)

The IRC listener relayed only the first line of a PRIVMSG or NOTICE
body; it now sends one line per body line. A relayed MODE change now
carries its key, limit or mask, each value its own parameter, also in
the echo to the user who made it. CR, LF and NUL are removed from each
parameter and from each whole line sent to an IRC listener connection,
so no stored value can start a line of its own. The channel name check
moved into service.JoinChannel, so the IRC listener's JOIN refuses the
same names with 403.

Model: opus-5-5
Co-authored-by: clawbot <sneak+clawbot@sneak.cloud>

internal/ircserver/parser.go

@@ -90,7 +90,10 @@ func ParseMessage(line string) *Message {
 }
 
 // FormatMessage formats an IRC message into wire protocol
-// format (without the trailing CR-LF).
+// format (without the trailing CR-LF). CR, LF and NUL are
+// removed from each parameter, because on the wire they would
+// end the line early; this happens before deciding whether
+// the last parameter needs a leading ':'.
 func FormatMessage(
 	prefix, command string,
 	params ...string,
@@ -106,6 +109,10 @@ func FormatMessage(
 	buf.WriteString(command)
 
 	for i, param := range params {
+		param = strings.ReplaceAll(param, "\r", "")
+		param = strings.ReplaceAll(param, "\n", "")
+		param = strings.ReplaceAll(param, "\x00", "")
+
 		buf.WriteByte(' ')
 
 		isLast := i == len(params)-1