feat(client): add Tag entity (get, create, save, dispatch)

[mekarpeles]

Summary

Adds ol.Tag as a first-class entity in openlibrary-client, alongside ol.Work, ol.Edition, and ol.Author.

OL Tags are Infogami documents at /tags/OLnT introduced in GSoC 2023. They provide a controlled vocabulary for subject tagging.

New API

ol = OpenLibrary()

# Fetch by OLID
tag = ol.Tag.get('OL32T')
# → Tag(olid='OL32T', name='cooking', tag_type='subject', ...)

# Generic dispatch (works via the 'T' suffix)
tag = ol.get('OL32T')

# Save a change
tag.tag_description = "Updated description"
tag.save("update description")

# Create a new tag (requires auth + save_many)
ol.Tag.create('science_fiction', 'subject', 'Works of speculative fiction')

# Serialize to OL JSON
tag.json()
# → {'key': '/tags/OL32T', 'type': {'key': '/type/tag'}, 'name': 'cooking', ...}

What's included

• ol.Tag property (dynamic class factory, same pattern as Work/Edition/Author)
• Tag.get(olid) — fetches /tags/{olid}.json, returns None if not found
• Tag.create(name, tag_type, description, comment) — via save_many
• tag.save(comment) — PUT /tags/{olid}.json
• tag.json() — excludes read-only fields (olid, revision, latest_revision, created, last_modified), adds key and type
• ol.get('OL32TÈ') dispatch via the T suffix
• olclient/schemata/tag.schema.json — based on /type/tag and real OL documents

Testing

pytest tests/ -x -q
53 passed (7 new Tag tests)

New tests cover: Tag.__init__, tag.json(), Tag.get(), Tag.get() returns None for missing tags, ol.get() dispatch to Tag.

Related

Part of the openlibrary-client improvement series (PR 5 of 5):

• PR fix(schema): replace deprecated jsonschema.RefResolver with referencing.Registry #438: Fix CI deprecations (merged)
• PR feat(client): add from_local(), env var credentials, health_check() #439: Local dev ergonomics (open)
• PR feat(client): add get_many() and get_many_by_isbn() bulk fetch #440: Bulk fetch get_many() (open)
• PR test(client): add integration test infrastructure #441: Integration test infrastructure (open)
• This PR: Tag entity