feat(deps)!: make all de/serialization libraries optional

[jkowalleck]

when using this library for validation, i dont need to have the de/serialization dependencies installed.

goal

make all de/serialization libraries optional

solution

• make de/serialization dependnecies optional, and installable in an extra called "de/serialization" orsomething
• have a private module that tries to load optional de/serialization libs, and if this fails, then provide stubs.
• runtime shall not use any de/serialization dependencies directly, but use the own optionally loaded ones (see above)

possible implementation (pseudo)

# file: _opt/serialization.py

__all__ = ['Serializer']

try:
  from serializaers import Serializer
except:
  # stubs
  class Serializer:
    def to_json() -> Never:
      raise Error('missing serializer, install optional dependnecy "serializaers"')
    def from_json() -> Never:
      raise Error('missing serializer, install optional dependnecy "serializaers"')

# file: models/bom.py

from .._opt.serialization import Serializer

class Bom(Serializer):
  ...