Refactor cfg config parsing and add toml format

[tdrwenski]

This PR refactors the configuration and adds a toml format for the config.

The goal of the config refactor is to move all configuration validation and defaults to a central location (Config). This will be useful when moving the python interface to use nanobind.

In addition it adds a toml format (while keeping the current cfg format). We would like to phase out the cfg format once the python interface uses nanobind. The toml format is parsed using the tomlplusplus library, and the used settings when running quandary (regardless of input bring cfg or toml) will be written as data_dir/config_log.toml, which can help in transitioning from cfg to toml.