Consider reducing default dependencies even more

[roll]

Overview

In the initial version, the default installation provides all the based descriptor and model functions including JSONSchema validation (jsonschema dep), remote loading (fsspec dep), and YAML support (pyyaml dep).

As the library needs to be used in other systems as a metadata mapper, we might consider limiting the bare installation only to pydantic dependency as the dependencies mentioned above are not needed for metadata mapping. They can be moved behind e.g. dplib-py[base] optional dependencies group