Fix bazel build, and commit module lock file.

Including:
- Remove WORKSPACE and upgrade to MODULE.bazel.
- The integration tests were not included since the directory was misspelled.
- Their header files were not accessible.

test/integration/handler_test.h

@@ -0,0 +1,32 @@
+#include "mock_event_handler.h"
+#include "yaml-cpp/yaml.h"  // IWYU pragma: keep
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+using ::testing::InSequence;
+using ::testing::NiceMock;
+using ::testing::StrictMock;
+
+namespace YAML {
+class HandlerTest : public ::testing::Test {
+ protected:
+  void Parse(const std::string& example) {
+    std::stringstream stream(example);
+    Parser parser(stream);
+    while (parser.HandleNextDocument(handler)) {
+    }
+  }
+
+  void IgnoreParse(const std::string& example) {
+    std::stringstream stream(example);
+    Parser parser(stream);
+    while (parser.HandleNextDocument(nice_handler)) {
+    }
+  }
+
+  InSequence sequence;
+  StrictMock<MockEventHandler> handler;
+  NiceMock<MockEventHandler> nice_handler;
+};
+}