Validate Rust tensor element types (#32035)
This pull request improves how tensor element types are handled in the
ONNX Runtime Rust bindings. It introduces more robust error handling for
unsupported and undefined tensor element types, replacing previous
unchecked conversions with a safe and explicit conversion mechanism. The
most important changes are:
**Error Handling Improvements:**
* Added a new `OrtError::UnsupportedTensorElementType(i64)` variant to
represent unsupported tensor types, and updated the
`UndefinedTensorElementType` error message for clarity.
**Type Conversion and Safety:**
* Implemented `TryFrom<sys::ONNXTensorElementDataType>` for
`TensorElementDataType`, returning descriptive errors for undefined or
unsupported types instead of using unsafe `transmute`.
* Updated code in `dangerous` module to use the new `try_from`
conversion for tensor element types, eliminating unsafe casting and
ensuring errors are handled explicitly.
**Testing:**
* Added unit tests to verify that supported types convert successfully,
undefined types return the correct error, and unsupported types are
properly rejected.
**Code Cleanliness:**
* Added necessary imports for `TryFrom` in `session.rs` to support the
new conversion logic.
