address flagBuffer ownership issue (#749)

This pull request updates the handling of the default flag buffer in the
C++ and Python bindings to ensure proper memory management when
interfacing with Python.

Make sure the buffer will not be deallocated when transfer ownership
from cpp to python

include/mscclpp/algorithm.hpp

@@ -366,7 +366,7 @@ class AlgorithmCollection {
 
 /// Get a default GPU flag buffer (allocated once and reused).
 /// @return A pair of (shared_ptr to the flag buffer, size in bytes).
-std::pair<std::shared_ptr<void>, size_t> getDefaultFlagBuffer();
+std::pair<std::shared_ptr<void>, size_t> getFlagBuffer();
 
 }  // namespace mscclpp