Add future annotations as some modules fail with Python 3.9

.github/pull_request_template.md

@@ -25,5 +25,6 @@ Otherwise, please check the following TODO list:
 - [ ] Replace `<COPYRIGHT HOLDER>` in `LICENSE` of your package with your name
 - [ ] Fill out `README.md` in your package
 - [ ] Add import statements of your function or class names to be used in `__init__.py`
+- [ ] (Optional) Add `from __future__ import annotations` at the head of any Python files that include typing to support older Python versions
 - [ ] Apply the formatter based on the tips in [`README.md`](https://github.com/optuna/optunahub-registry/tree/main)
 - [ ] Check whether your module works as intended based on the tips in [`README.md`](https://github.com/optuna/optunahub-registry/tree/main)

package/samplers/nelder_mead/generate_initial_simplex.py

@@ -22,6 +22,8 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 
+from __future__ import annotations
+
 import numpy as np
 
 

package/samplers/plmbo/plmbo.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from typing import Any
 
 import GPy