extract TerminalHandler from FilterChain into a interface

Author: Ericthilen

src/main/java/org/example/server/FilterChain.java

@@ -3,10 +3,6 @@
 import java.util.Objects;
 
 public final class FilterChain {
-    @FunctionalInterface
-    public interface TerminalHandler {
-        void handle(HttpRequest request, HttpResponse response);
-    }
 
     private final HttpFilter[] filters;
     private final TerminalHandler terminal;