Support mypy v0.990 new Optional report

.pre-commit-config.yaml

duniterpy/api/bma/blockchain.py

duniterpy/api/endpoint.py

duniterpy/documents/block.py

duniterpy/documents/certification.py

duniterpy/documents/identity.py

duniterpy/documents/membership.py

duniterpy/documents/peer.py

duniterpy/documents/revocation.py

duniterpy/grammars/output.py

duniterpy/key/signing_key.py