Add type annotations to swh.core.api

Files swh/core/api/negotiation.py and swh/core/api/serializers.py currently do not have any type annotation. It would be nice to annotate all their functions.

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Migrated from T2256 (view on Phabricator)

marked this issue as related to #2255

added Core & foundations Easy hack priority:Low labels

changed title from Add type annotations to swh.core.api.negotiation to Add type annotations to swh.core.api

changed the description

assigned to @legau

closed