Automated fix by @leftibot.

What changed

Fix #594: Map keys become dangling references when pushed into Vector
The Handle_Return_Ref specialization for const references was wrapping
return values in std::cref() while marking them as return values
(is_return_value=true). This caused Vector.push_back() to store the
reference directly without cloning, since it assumes return values are
freshly created temporaries. When the source object (e.g., a map) went
out of scope, the vector contained dangling references to freed memory.
The fix sets is_return_value=false for const reference returns, which
correctly triggers push_back to clone the value instead of storing a
bare reference. This is consistent with the non-const reference handler
(Handle_Return<Ret &>) which also does not set the return value flag.
Co-Authored-By: Claude Opus 4.6 (1M context) [email protected]

Files

 include/chaiscript/dispatchkit/handle_return.hpp |  2 +-
 unittests/map_keys_vector_push_back.chai         | 29 ++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

Closes #594

Triggered by @lefticus.