Add mock-based test suite for cuFile wrapper

This test suite uses mocked cuFile library functions to verify correct
API usage without requiring NVIDIA GPU hardware or the cuFile library.

The tests cover:
- CuFileDriver initialization and singleton pattern
- CuFile initialization with various file modes
- Open/close operations and handle registration
- Context manager functionality
- Read/write operations with correct argument passing
- Complete operation sequences
- Error handling for cuFile API failures
- Utility methods like get_handle()
- Direct testing of bindings layer functions

Author: yanok