Remove unused imports and make exports explicit

This allows Pyright to actually catch these errors, which would be
useful for CI purposes in the future.

pyproject.toml

@@ -42,6 +42,7 @@ exclude = [
     "docs",
 ]
 reportUnnecessaryTypeIgnoreComment = "warning"
+reportUnusedImport = "error"
 pythonVersion = "3.8"
 typeCheckingMode = "basic"