Stream-level masks should always override globally-set masks.
Next-kernel masks should always override both stream-level masks
and globally-set masks.

Tests reveal an issue with the next-kernel mask not overriding the
stream mask on CUDA 11.0+. CUDA appears to apply the per-stream
mask to the QMD/TMD after `launchCallback()` is triggered, making
it impossible to override as currently implemented.

Also rewrite the global masking test to be much more thorough.

Initially supports the GPU information functions via:
- pysmctrl.get_gpc_info(dev_id)
- pysmctrl.get_tpc_info(dev_id)
- pysmctrl.get_tpc_info_cuda(cuda_dev_id)
All functions are extensively documented. See pysmctrl/__init__.py
for details.

Device partitioning functions have yet to be mapped into Python, as
these will require more testing.

As part of this:
- libsmctrl_get_*_info() functions have been modified to consistently
  return positive error codes.
- libsmctrl_get_tpc_info() now uses nvdebug-style device numbering and
  uses libsmctrl_get_gpc_info() under the covers. This should be more
  reliable.
- libsmctrl_get_tpc_info_cuda() has been introduced as an improved
  version of the old libsmctrl_get_tpc_info() function. This continues
  to use CUDA-style device numbering, but is now resiliant to CUDA
  failures.
- Various minor style improvements in libsmctrl.c

- Tested working with cuda_scheduling_examiner
- Supports everything described in the accepted RTAS'23 paper
- Can be used as either a shared or staticly-linked library
- Documented in libsmctrl.h