Remove cfg file format

[tdrwenski]

As a follow up to #100 which added a toml format for the config options, we would like to remove the cfg file format once all branches have transitioned to the new format. This includes removing (see TODO cfg throughout the code:

• cfg template, regression test files
• cfgparser and config_types classes

This depends on the python interface being changed to use nanobind instead of current implementation using cfg files (depends on #102)