[FEAT][RUST] Support runtime-checked try_cast between ObjectRef types

[Seven-Streams]

This PR adds direct, runtime-checked casting between Rust object handles, mirroring C++ ObjectRef::as<T> / Downcast<T>.

ObjectRefCast is blanket-implemented for types implementing both ObjectRefCore and AnyCompatible. try_cast::<B>(self) consumes the source and, on success, rewraps the same object as B without cloning or copying it. A failed cast returns a TypeError describing the source and target types.

Target compatibility is delegated to B::check_any_strict. ObjectRef hierarchies accept B and its runtime subtypes, while parameterized containers use their complete type semantics.

let base: TestBase = derived.try_cast()?; // upcast
let obj: ObjectRef = base.try_cast()?;    // upcast to root
let d: TestDerived = obj.try_cast()?;     // checked downcast

The direct A -> B path reuses the existing AnyCompatible conversion traits through a raw TVMFFIAny, so callers do not need to construct an Any or AnyView. It first creates a non-owning view for the target check and transfers ownership only after that check succeeds, keeping failure and panic paths leak-free.

Derived ObjectRef conversions preserve the runtime type index stored in the object header. A derived object upcast to a base handle can therefore still round-trip through Any or AnyView and downcast correctly.

A hidden is_instance_of helper provides hierarchy checks for derive-generated object containers. The cast path uses assert_unchecked after establishing the object type-index invariant; release codegen confirms that the intermediate TVMFFIAny storage and redundant object-range check are eliminated.

The PR also includes the derive fixes required by downstream crates and focused tests covering hierarchy casts, failure ownership, dynamic-type preservation through Any/AnyView, direct try_cast_from_any_view, and parameterized-container mismatch.

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[Seven-Streams]

Why the order is changed

[tlopex]

We need the object pointer first because the type index is now read from the runtime object header instead of ContainerType::type_index(), which preserves the dynamic subtype after an upcast.

[Seven-Streams]

not sure if it's necessary

[tlopex]

I think it is. this is the root object fast path. Every object-range type must cast to objectref, and the C++ uses the same range check while avoiding type-table lookups.

[tqchen]

given this is runtime check, likely not having the specialization is ok, depending on how freq conversion to ObjectRef is.

[tlopex]

agreed

[tqchen]

given this is runtime check, likely not having the specialization is ok, depending on how freq conversion to ObjectRef is.

[tqchen]

might worthcheck other template trick for target_type_index. Note in the case of C++ TargetType can be a type T, where things like type_depth can be directly queried as a compile time constant rather than runtime

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.