add sheet load time benchmark

benchmarks/spreadsheet-load.cpp

@@ -0,0 +1,33 @@
+#include <xlnt/xlnt.hpp>
+#include <chrono>
+#include <helpers/path_helper.hpp>
+
+namespace {
+using milliseconds_d = std::chrono::duration<double, std::milli>;
+
+void run_test(xlnt::path &const file, int runs = 10)
+{
+    std::cout << file.string() << "\n\n";
+
+    xlnt::workbook wb;
+    std::vector<std::chrono::steady_clock::duration> test_timings;
+
+    for (int i = 0; i < runs; ++i)
+    {
+        auto start = std::chrono::steady_clock::now();
+        wb.load(file);
+
+        auto end = std::chrono::steady_clock::now();
+        wb.clear();
+        test_timings.push_back(end - start);
+
+        std::cout << milliseconds_d(test_timings.back()).count() << " ms\n";
+    }
+}
+} // namespace
+
+int main()
+{
+    run_test(path_helper::benchmark_file("large.xlsx"));
+    run_test(path_helper::benchmark_file("very_large.xlsx"));
+}