Yaecs

Improve path not found error message
Solve parsing bug when a list and a mapping end at the same time

Solve bugs for registered methods with no tag

Solve bug when a list contains several mappings in a row.
Allow non-string keys in dictionaries.

Processing and setting of new params is now disentangled from the main Configuration object. It is not yet fully clean, but it's come a long way.

Harmonise all instances of adding attributes to methods or functions using the attribute yaecs_metadata.
Prepare the code to the disentanglement of the parameter processing.
Change processing function "copy_param"'s tag from "copy" to "copy_param"
Remove obsolete checks for unlinked configs.
Remove sub-config registration.
Move all type hints handling to the main config.
Refactor the core merging and adding operations.