System: Rewrite save state I/O

No more ByteStream or virtual calls for every piece of data.

src/common/string_util.cpp

@@ -124,6 +124,12 @@ std::size_t StringUtil::Strlcpy(char* dst, const char* src, std::size_t size)
   return len;
 }
 
+std::size_t StringUtil::Strnlen(const char* str, std::size_t max_size)
+{
+  const char* loc = static_cast<const char*>(std::memchr(str, 0, max_size));
+  return loc ? static_cast<size_t>(loc - str) : max_size;
+}
+
 std::size_t StringUtil::Strlcpy(char* dst, const std::string_view src, std::size_t size)
 {
   std::size_t len = src.length();

src/common/string_util.h

@@ -35,6 +35,9 @@ std::size_t Strlcpy(char* dst, const char* src, std::size_t size);
 /// Strlcpy from string_view.
 std::size_t Strlcpy(char* dst, const std::string_view src, std::size_t size);
 
+/// Bounds checked version of strlen.
+std::size_t Strnlen(const char* str, std::size_t max_size);
+
 /// Platform-independent strcasecmp
 static inline int Strcasecmp(const char* s1, const char* s2)
 {