Add from __future__ import annotations for Python 3.8 compatibility

The str | Path union type syntax requires Python 3.10+ but setup.py
declares python_requires>=3.8. This fixes the HuggingFace Spaces demo
which runs Python 3.8.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: PatBall1

detectree2/models/evaluation.py

@@ -2,6 +2,7 @@
 
 Classes and functions to evaluate model performances.
 """
+from __future__ import annotations
 import json
 import os
 from pathlib import Path

detectree2/models/outputs.py

@@ -3,6 +3,7 @@
 Funtions to process model predictions into outputs for model evaluation and
 mapping crowns in geographic space.
 """
+from __future__ import annotations
 import glob
 import json
 import re

detectree2/models/predict.py

@@ -2,6 +2,7 @@
 
 This module contains the code to generate predictions on tiled data.
 """
+from __future__ import annotations
 import json
 from pathlib import Path
 

detectree2/models/train.py

@@ -3,6 +3,7 @@
 Classes and functions to train a model based on othomosaics and corresponding
 manual crown data.
 """
+from __future__ import annotations
 import datetime
 import json
 import logging