If the backend was not closed properly, the former socket may still be present. This was
preventing the backend to start again, while now the old socket is removed in this case.
This is a huge configuration refactoring.
The configuration system now uses Pydantic settings, with better validation, better
support for environment variables and other goodies.
The main config files now use TOML instead of INI, this allow for better handling of
complex types, notably dict.
Plugins, components and frontends can declare their config settings in a class which will
be imported dynamically.
