Add "local" chat channels with proximity-based messaging

Introduced a "local" channel type to restrict chat visibility based on player proximity, configurable via `LOCAL_DISTANCE`. Added channel spy functionality to monitor "local" messages. Updated constructors and configuration to support this new feature.

api/src/main/java/com/alttd/chat/objects/channels/Channel.java

@@ -10,12 +10,14 @@ public class Channel {
     protected String channelName;
     protected String format;
     protected boolean proxy;
+    protected boolean local;
 
-    public Channel(String channelName, String format, boolean proxy) {
+    public Channel(String channelName, String format, boolean proxy, boolean local) {
         this.permission = "chat.channel." + channelName.toLowerCase();
         this.channelName = channelName;
         this.format = format;
         this.proxy = proxy;
+        this.local = local;
         channels.put(channelName.toLowerCase(), this);
     }
 
@@ -39,6 +41,10 @@ public class Channel {
         return proxy;
     }
 
+    public boolean isLocal() {
+        return local;
+    }
+
     public static Channel getChatChannel(String channelName) {
         return channels.get(channelName.toLowerCase());
     }

api/src/main/java/com/alttd/chat/objects/channels/CustomChannel.java

@@ -5,8 +5,8 @@ import java.util.*;
 public class CustomChannel extends Channel {
     private final List<String> servers;
 
-    public CustomChannel(String channelName, String format, List<String> servers, boolean proxy) {
-        super(channelName, format, proxy);
+    public CustomChannel(String channelName, String format, List<String> servers, boolean proxy, boolean local) {
+        super(channelName, format, proxy, local);
         this.permission = "chat.channel." + channelName.toLowerCase();
         this.channelName = channelName;
         this.format = format;

api/src/main/java/com/alttd/chat/objects/channels/DefaultChannel.java

@@ -2,6 +2,6 @@ package com.alttd.chat.objects.channels;
 
 public abstract class DefaultChannel extends Channel{
     public DefaultChannel(String channelName, String format, boolean proxy) {
-        super(channelName, format, proxy);
+        super(channelName, format, proxy, false);
     }
 }