[breaking] Bump Python requirement to 3.10. (#10434)

- Bump the Python requirement.
- Fix type hints.
- Use loky to avoid deadlock.
- Workaround cupy-numpy compatibility issue on Windows caused by the `safe` casting rule.
- Simplify the repartitioning logic to avoid dask errors.

demo/guide-python/quantile_data_iterator.py

@@ -42,7 +42,7 @@ class IterForDMatrixDemo(xgboost.core.DataIter):
         """
         self.rows = ROWS_PER_BATCH
         self.cols = COLS
-        rng = cupy.random.RandomState(1994)
+        rng = cupy.random.RandomState(numpy.uint64(1994))
         self._data = [rng.randn(self.rows, self.cols)] * BATCHES
         self._labels = [rng.randn(self.rows)] * BATCHES
         self._weights = [rng.uniform(size=self.rows)] * BATCHES