Automated fix by @leftibot.

What changed

Fix #374: Support nested vector type conversions
vector_conversion's element conversion used Cast_Helper directly, which
only performs exact type matching. For nested vectors like
std::vector<std::vector>, each inner element is a
std::vector<Boxed_Value> that needs its own conversion to
std::vector. Added a recursive convert_vector_element helper
that detects std::vector value types and converts them from
std::vector<Boxed_Value> before falling back to Cast_Helper for
leaf types.
Co-Authored-By: Claude Opus 4.6 (1M context) [email protected]

Files

 .../chaiscript/dispatchkit/type_conversions.hpp    | 25 ++++++++++++++++++-
 unittests/compiled_tests.cpp                       | 29 ++++++++++++++++++++++
 2 files changed, 53 insertions(+), 1 deletion(-)

Closes #374

Triggered by @lefticus.