Reimplement autoproxy escape character

PluralKit.Bot/Proxy/ProxyMatcher.cs

@@ -9,6 +9,7 @@ namespace PluralKit.Bot
 {
     public class ProxyMatcher
     {
+        private static readonly char AutoproxyEscapeCharacter = '\\';
         private static readonly Duration LatchExpiryTime = Duration.FromHours(6);
 
         private readonly IClock _clock;
@@ -42,6 +43,10 @@ namespace PluralKit.Bot
         {
             match = default;
 
+            // Skip autoproxy match if we hit the escape character
+            if (messageContent.StartsWith(AutoproxyEscapeCharacter))
+                return false;
+
             // Find the member we should autoproxy (null if none)
             var member = ctx.AutoproxyMode switch
             {