spdlog: fmt - support `std::span` in `to_hex`

`std::span` does not have `const_iterator`. this prevents `to_hex` from
being used with `std::span<>`. to fix this, we provide an explicit
overload.

compare: https://cplusplus.github.io/LWG/issue3320

include/spdlog/fmt/bin_to_hex.h

@@ -8,6 +8,14 @@
 #include <cctype>
 #include <spdlog/common.h>
 
+#if defined(__has_include) && __has_include(<version>)
+#include <version>
+#endif
+
+#if __cpp_lib_span >= 202002L
+#include <span>
+#endif
+
 //
 // Support for logging binary data as hex
 // format flags, any combination of the following:
@@ -68,6 +76,19 @@ inline details::dump_info<typename Container::const_iterator> to_hex(const Conta
     return details::dump_info<Iter>(std::begin(container), std::end(container), size_per_line);
 }
 
+#if __cpp_lib_span >= 202002L
+
+template <typename Value, size_t Extent>
+inline details::dump_info<typename std::span<Value, Extent>::iterator> to_hex(const std::span<Value, Extent> &container, size_t size_per_line = 32)
+{
+    using Container = std::span<Value, Extent>;
+    static_assert(sizeof(typename Container::value_type) == 1, "sizeof(Container::value_type) != 1");
+    using Iter = typename Container::iterator;
+    return details::dump_info<Iter>(std::begin(container), std::end(container), size_per_line);
+}
+
+#endif
+
 // create dump_info from ranges
 template<typename It>
 inline details::dump_info<It> to_hex(const It range_begin, const It range_end, size_t size_per_line = 32)