Began working on mfem_resolver formatters

src/include/serif/utils/format/strings.hpp

@@ -0,0 +1,19 @@
+#pragma once
+#include <string>
+#include <string_view>
+#include <span>
+#include <format>
+#include <type_traits>
+
+namespace serif::utils::misc::format {
+    template <typename T>
+    std::string join(const std::span<T>& elements, std::string_view delimiter)
+    {
+        std::string out;
+        for (const auto& element : elements) {
+            out = std::format("{}{}{}", out, delimiter, element);
+        }
+
+        return out;
+    }
+}