Fixes precision loss when adding nested models.

The precision loss is resolved by explicitly calling std::setprecision
for float and double parameters when these are streamed/requested as
strings.

include/sdf/Param.hh

@@ -23,6 +23,7 @@
 #include <cctype>
 #include <cstdint>
 #include <functional>
+#include <iomanip>
 #include <memory>
 #include <optional>
 #include <sstream>
@@ -79,6 +80,20 @@ namespace sdf
     return os;
   }
 
+  template<>
+  inline std::ostream& operator<<(std::ostream &os, ParamStreamer<double> s)
+  {
+    os << std::setprecision(std::numeric_limits<double>::max_digits10) << s.val;
+    return os;
+  }
+
+  template<>
+  inline std::ostream& operator<<(std::ostream &os, ParamStreamer<float> s)
+  {
+    os << std::setprecision(std::numeric_limits<float>::max_digits10) << s.val;
+    return os;
+  }
+
   template<class... Ts>
   std::ostream& operator<<(std::ostream& os,
                            ParamStreamer<std::variant<Ts...>> sv)