C++/Embedded: don't use std::format

This makes the code size quite large - instead fall back to
snprintf(), which is plenty sufficient for our needs.

cpp/src/CMakeLists.txt

@@ -1,12 +1,10 @@
 set(monoformat_SOURCES
     monoformat_schema.cpp
-    monoformat_structured.cpp
     monoformat_parseonly.cpp
     monoformat_fontreader.cpp
 )
 set(monoformat_HEADERS
     monoformat_schema.hpp
-    monoformat_structured.hpp
     monoformat_parsehelpers.hpp
     monoformat_parseonly.hpp
     monoformat_fontreader.hpp
@@ -14,6 +12,18 @@ set(monoformat_HEADERS
     monoformat_utf8.hpp
 )
 
+option(MONOFORMAT_EMBEDDED "Only build for embedded devices" FALSE)
+
+if(NOT MONOFORMAT_EMBEDDED)
+    list(APPEND monoformat_SOURCES
+        monoformat_structured.cpp
+    )
+
+    list(APPEND monoformat_HEADERS
+        monoformat_structured.hpp
+    )
+endif()
+
 add_library(monoformat ${monoformat_SOURCES} ${monoformat_HEADERS})
 target_compile_features(monoformat PUBLIC cxx_std_23)
 target_include_directories(monoformat PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})

cpp/src/monoformat_parseonly.cpp

@@ -4,7 +4,7 @@
 
 #include <string_view>
 #include <string>
-#include <format>
+#include <cstdio>
 #include <iostream>
 
 namespace monoformat {
@@ -1029,17 +1029,19 @@ std::expected<void, ParseError> handleCurrentTime(std::span<std::byte const>& bu
         }
     }
 
-    std::string text;
+    char text[32] = {};
     if (showHours && showMinutes && showSeconds) {
-        text = std::format("{:02d}:{:02d}:{:02d}", hours, minutes, seconds);
+        std::snprintf(text, sizeof(text), "%02d:%02d:%02d", int(hours), int(minutes), int(seconds));
     } else if (showHours && showMinutes) {
-        text = std::format("{:02d}:{:02d}", hours, minutes);
+        std::snprintf(text, sizeof(text), "%02d:%02d", int(hours), int(minutes));
     } else if (showHours) {
-        text = std::format("{:02d}", hours);
+        std::snprintf(text, sizeof(text), "%02d", int(hours));
     } else if (showMinutes && showSeconds) {
-        text = std::format("{:02d}:{:02d}", minutes, seconds);
+        std::snprintf(text, sizeof(text), "%02d:%02d", int(minutes), int(seconds));
     } else if (showSeconds) {
-        text = std::format("{:02d}", seconds);
+        std::snprintf(text, sizeof(text), "%02d", int(seconds));
+    } else if (showMinutes) {
+        std::snprintf(text, sizeof(text), "%02d", int(minutes));
     } else {
         return {};
     }