Fix Python 3.8 compatibility: Use typing.Tuple instead of tuple[]

ISSUE:
Python 3.8 doesn't support PEP 585 generic type hints (tuple[...], list[...], etc.)
Error: TypeError: 'type' object is not subscriptable

CHANGE:
- Import Tuple from typing module
- Change 'tuple[int, str, str]' to 'Tuple[int, str, str]'

COMPATIBILITY:
- Works on Python 3.8+ (typing.Tuple available since 3.5)
- All 950 tests pass

This fixes CI failures on Python 3.8 builds.

Author: claude

tests/unit/test_crash_isolation.py

@@ -9,10 +9,11 @@
 import subprocess
 import sys
 import textwrap
+from typing import Tuple
 import pytest
 
 
-def run_in_subprocess(code: str) -> tuple[int, str, str]:
+def run_in_subprocess(code: str) -> Tuple[int, str, str]:
     """Run code in a subprocess and return exit code, stdout, stderr.
 
     Returns: