Add type annotations #1331

Job	Run time
🐍 Prepare Python	24s
⬢ Prepare Node.js	16s
🔍 Check if pull request	2s
🧱 Build test matrix	9s
🧱 Build Spotlight	2m 23s
🔍 Check	2m 29s
📝 Build API docs	38s
🗃 Build datasets	1m 58s
🧪 Doc Test	1m 34s
🧪 Unit Test	1m 13s
🔍 Check wheel contents	33s
🧪 UI Test (chrome)	2m 37s
🧪 Integration Test (ubuntu-latest, 3.8)	10m 41s
🧪 UI Test (firefox)	3m 20s
🚀 Release Spotlight	0s
	28m 17s

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