Create a "pretty printer" for the VTR .net file format

The VTR [packed XML `.net` is hard to read](https://vtr-verilog-to-routing.readthedocs.io/en/latest/vpr/file_formats.html#packed-netlist-format-net).

It would be good if we had a Python based tool that printed more human readable output. You can take inspiration from how [utils/print_graph.py](utils/print_graph.py) tries to make the `rr_graph.xml` format easier to read.