Add pyproject dependency on scikit-learn

It is a de-facto requirement due to use in ingestion. We might relax it to optional again if we have better import guards with a clear message.

Author: ihnorton

apis/python/pyproject.toml

@@ -21,11 +21,12 @@ classifiers = [
 dependencies = [
     "tiledb-cloud>=0.10.5",
     "tiledb>=0.15.2",
-    "typing-extensions" # for tiledb-cloud indirect
+    "typing-extensions", # for tiledb-cloud indirect, x-ref https://github.com/TileDB-Inc/TileDB-Cloud-Py/pull/428
+    "scikit-learn",
 ]
 
 [project.optional-dependencies]
-test = ["pytest", "scikit-learn", "tiledb-cloud"]
+test = ["pytest"]
 
 
 [project.urls]