Minor Refactoring of CodecManager

[LTMeyer]

This PR refactors several small bits of the CodecManager.

• Remove pydantic dependency by the use of dataclass. (pydantic is great if we actually perform some type checks, and this comes with more complex configuraiton). Standard libary dataclass is perfectly suited for our use case.
• It improves typing by introducing CodecHFConfig, CodecType, ModalityTypeError, and TokenKeyError
• Use lru_cache to cache both access to HF models (note that they are cached by default in the HF library), and codec retrieval from modality
• Move codec to device only in the encode/decode method. Otherwise GPU memory could be saturated if too many codecs were loaded.

[EiffL]

hummm, but would the following work in this approach:

from aion.modalities import LegacySurveyImage

print(LegacySurveyImage.name)

i.e. accessing class variables, without instantiating the class?

[LTMeyer]

hummm, but would the following work in this approach:

from aion.modalities import LegacySurveyImage

print(LegacySurveyImage.name)

i.e. accessing class variables, without instantiating the class?

Hmm. Just for me to understand. We only instantiate modalities when returned and when we populate the values field, otherwise we use the object type right?

[LTMeyer]

i.e. accessing class variables, without instantiating the class?

Sure we can (see https://docs.python.org/3/library/typing.html#typing.ClassVar). What is the need again?