Explore `#line` directives for Python/SASS mappings

https://gcc.gnu.org/onlinedocs/cpp/Line-Control.html

Add line directives in the generated CUDA-C code, e.g.

```
#line 55 "warp_kernel.py"
```

instead of

```
// wp.atomic_add(loss, 0, delta)
<L 55>
```

This might allow us to correlate the Python code to the SASS.