chore: add structurally typed GenericPythonConfiguration (#1458)

* Add structually typed GenericPythonConfiguration

Use structural typing for the return value of get_python_configurations
so that we don't have to specify a union of all possible PythonConfiguration
types

* address henryiii's comments

* Use Set in more places

cibuildwheel/linux.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 import subprocess
 import sys
 import textwrap
+from collections.abc import Set
 from dataclasses import dataclass
 from pathlib import Path, PurePath, PurePosixPath
 from typing import Iterator, Tuple
@@ -46,7 +47,7 @@ class BuildStep:
 
 def get_python_configurations(
     build_selector: BuildSelector,
-    architectures: set[Architecture],
+    architectures: Set[Architecture],
 ) -> list[PythonConfiguration]:
     full_python_configs = read_python_configs("linux")