Rewrite the core C++ type registration and FFI dispatch layer from
crates/bindings-cpp in Rust. The new crate provides:

- ModuleTypeRegistration: full SATS type registration with circular
  reference detection, error module generation, and BSATN serialization
- FFI dispatch: __describe_module__, __call_reducer__, __call_view__,
  __call_view_anon__, __call_procedure__ with proper Identity/ConnectionId
  reconstruction and BytesSource/BytesSink I/O
- Preinit functions: __preinit__01_clear_global_state and
  __preinit__99_validate_types matching the C++ originals

Replaces ~1,414 lines of C++ with ~1,139 lines of Rust (19% reduction)
plus 96 unit tests (100% coverage). Clippy-clean and fmt-clean.

Previously, `spacetime version uninstall <ver>` would show a y/N
confirmation prompt even when the version wasn't installed, then fail
with a cryptic "No such file or directory (os error 2)" after the user
confirmed.

Now the command checks if the version directory exists before prompting,
and returns a clear error: "v{ver} is not installed".

Added 4 unit tests covering:
- Nonexistent version errors before prompt
- Current version cannot be uninstalled
- "current" keyword cannot be uninstalled
- Successful uninstall removes the version directory

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>