feat(add solutions reference for challenge 01-concurrent-aggregator)

Makefile

@@ -0,0 +1,17 @@
+test:
+	go run gotest.tools/gotestsum@latest --format=testdox  -- -covermode=atomic -coverprofile=coverage.txt ./...
+benchmark:
+	go test -bench=. -benchmem ./...
+format:
+	go fmt ./...
+format-check:
+	@UNFORMATTED_FILES=$$(gofmt -l .); \
+	if [ -n "$$UNFORMATTED_FILES" ]; then \
+		echo "::error::The following files are not formatted correctly:"; \
+		echo "$$UNFORMATTED_FILES"; \
+		echo "--- Diff ---"; \
+		gofmt -d .; \
+		exit 1; \
+	fi
+
+.PHONY: test format benchmark format-check