- Changed import path from `h3result.cffi` to `h3result._cffi` in
`build_ext.py`, `error.py`, `h3result.py`, and `read_h3result.py`.
- Added import of `_cffi_backend` in `__init__.py` to ensure compatibility
with PyInstaller.
- Updated `cffi` dependency version in `pyproject.toml` to "^1.17".
- Bumped package version to "1.0.2" in `pyproject.toml`.

These changes were made to resolve potential import issues and ensure the
package is up-to-date with dependency requirements. Import path adjustments
improve modular access and compatibility, while the version change indicates
enhancements without breaking changes.