Replace nlohmann/json with native C++20 JSON engine, cut build RAM/time, fix 32-bit build, enable -O2 -march=native

util.cpp

@@ -324,6 +324,37 @@ int to_int_val(std::string_view s, int def) {
   return (int)v;
 }
 
+bool read_file_str(std::string_view path, std::string &out) {
+  out.clear();
+  std::string p(path);
+  FILE *f = std::fopen(p.c_str(), "rb");
+  if (!f) return false;
+  char buf[4096];
+  size_t n;
+  while ((n = std::fread(buf, 1, sizeof buf, f)) > 0) {
+    out.append(buf, n);
+  }
+  bool ok = (std::ferror(f) == 0);
+  std::fclose(f);
+  return ok;
+}
+
+bool write_file_str(std::string_view path, std::string_view data) {
+  std::string p(path);
+  FILE *f = std::fopen(p.c_str(), "wb");
+  if (!f) return false;
+  size_t written = 0;
+  while (written < data.size()) {
+    size_t n = std::fwrite(data.data() + written, 1, data.size() - written, f);
+    if (n == 0) {
+      std::fclose(f);
+      return false;
+    }
+    written += n;
+  }
+  return std::fclose(f) == 0;
+}
+
 /* ----------------------------- signal --------------------------------- */
 static void sigint_handler(int sig) {
   (void)sig;