Make fail fast abort the whole run.

src/run.cpp

@@ -87,6 +87,11 @@ namespace fuc2 {
 
     for(auto& test : tests) {
       fail_count += run(test, opts, argc > 1);
+
+      if(opts.fail_fast && fail_count > 0) {
+        fmt::println("FAIL FAST! Aborting early.");
+        break;
+      }
     }
 
     return fail_count;