feat!: Expose Value handles across FFI and managed bindings

- extend FFI result metadata and add regorus::Value creation, cloning, JSON, and engine wiring APIs via a new value module
- introduce managed Value wrapper, shared UTF-8 helpers, engine methods, and MSTest coverage in the C# package
- add regorus_value.hpp smoke test for C++ bindings and align .NET consumers with the 0.8.1 package
- refresh dependent Cargo.lock files after the new exports

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

Author: anakrish