add getModulus() to match setModulus used in the private server plugin. (#3043)

runelite-api/src/main/java/net/runelite/api/Client.java

@@ -2036,6 +2036,8 @@ public interface Client extends GameEngine
 
 	void setModulus(BigInteger modulus);
 
+	BigInteger getModulus();
+
 	/**
 	 * Returns the max item index + 1 from cache
 	 */

runelite-mixins/src/main/java/net/runelite/mixins/RSClientMixin.java

@@ -1922,6 +1922,13 @@ public abstract class RSClientMixin implements RSClient
 		RSClientMixin.modulus = modulus;
 	}
 
+	@Inject
+	@Override
+	public BigInteger getModulus()
+	{
+		return RSClientMixin.modulus;
+	}
+
 	@Copy("forceDisconnect")
 	@Replace("forceDisconnect")
 	@SuppressWarnings("InfiniteRecursion")

runescape-api/src/main/java/net/runelite/rs/api/RSClient.java

@@ -1127,6 +1127,8 @@ public interface RSClient extends RSGameEngine, Client
 
 	void setModulus(BigInteger modulus);
 
+	BigInteger getModulus();
+
 	@Import("ItemDefinition_fileCount")
 	int getItemCount();