- Use strong types in .pxd (ObjectCode, KernelOccupancy)
- Remove cdef public - attributes now private to C level
- Add Kernel.handle property for external access
- Add ObjectCode.symbol_mapping property (symmetric with input)
- Update _launcher.pyx, _linker.py, tests to use public APIs

- Module globals: _inited, _py_major_ver, _py_minor_ver, _driver_ver,
  _kernel_ctypes, _paraminfo_supported -> cdef typed
- Module functions: _lazy_init, _get_py_major_ver, _get_py_minor_ver,
  _get_driver_ver, _get_kernel_ctypes, _is_paraminfo_supported,
  _make_dummy_library_handle -> cdef inline with exception specs
- Module constant: _supported_code_type -> cdef tuple
- Kernel._get_arguments_info -> cdef tuple

Note: KernelAttributes remains a regular Python class due to
segfaults when converted to cdef class (likely due to weakref
interaction with cdef class properties).

Follow the _MemPoolAttributes pattern:
- cdef class with inline cdef attributes (_kernel_weakref, _cache)
- _init as @classmethod (not @staticmethod cdef)
- _get_cached_attribute and _resolve_device_id use except? -1
- Explicit cast when dereferencing weakref

Extends the RAII handle system to support CUlibrary and CUkernel driver
objects used in _module.pyx. This provides automatic lifetime management
and proper cleanup for library and kernel handles.

Changes:
- Add LibraryHandle/KernelHandle types with factory functions
- Update Kernel, ObjectCode, KernelOccupancy to use typed handles
- Move KernelAttributes cdef block to .pxd for strong typing
- Update _launcher.pyx to access kernel handle directly via cdef

Replaces Python-level driver API calls with low-level cydriver calls
wrapped in nogil blocks for improved performance. This allows the GIL
to be released during CUDA driver operations.

Changes:
- cuDriverGetVersion, cuKernelGetAttribute, cuKernelGetParamInfo
- cuOccupancy* functions (with appropriate GIL handling for callbacks)
- cuKernelGetLibrary
- Update KernelAttributes._get_cached_attribute to use cydriver types

Four tests in test_utils.py relied on CuPy implicitly creating a CUDA
context but failed when pytest-randomly ordered them after tests using
the init_cuda fixture, which pops the context on cleanup.