Validate yaml files with schema

[sgoudham]

Currently, we're casting our retrieved data into types which is something we opted for as a fast and easy solution.

Going forward, we should perform schema validation on the returned data, as we do in catppuccin/catppuccin and catppuccin/userstyles.

[sgoudham]

Schema is validated upstream at catppuccin/catppuccin, we can trust that since its our own datasource and also nice to not duplicate the effort on both sides.