fix: str() => cstr() in cstringstream

kernel/src/CppLib/Stream.cpp

@@ -76,6 +76,6 @@ kcp::cstringstream& kcp::cstringstream::operator<<(base nb)
     current_base = nb;
 }
 
-const char* kcp::cstringstream::str() {
+const char* kcp::cstringstream::cstr() {
     return this->string;
 }

kernel/src/CppLib/Stream.hpp

@@ -38,6 +38,6 @@ namespace kcp {
 
         cstringstream& operator<<(base nb);
 
-        const char* str();
+        const char* cstr();
     };
 };