[FEAT][RUST]Add tvm_ffi::optional in Rust

[Seven-Streams]

This PR supports ffi::optionalPod, ffi::optionalStr in Rust. It keeps the same memory layout as C++'s ffi::optional.

[gemini-code-assist]

Code Review

This pull request introduces Rust stub generation capabilities to tvm-ffi-stubgen, allowing the automatic creation of typed Rust bindings (including structs, builders, and methods) from C++ reflection metadata. It also adds a layout-mirror Optional type in Rust to support C++ ffi::Optional fields. The feedback highlights two key issues: first, the Optional type automatically infers as !Send and !Sync due to its UnsafeCell field, which should be fixed by manually implementing these traits when T is thread-safe; second, a potential ZeroDivisionError in the alignment calculation within the Python codegen should be prevented by ensuring the alignment value is at least 1.

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[Seven-Streams]