executors: use shutil.which instead of deprecated distutils

See PEP 632, which suggests replacing distutils.spawn.find_executable with shutil.which.

dmoj/executors/base_executor.py

@@ -6,7 +6,6 @@
 import sys
 import tempfile
 import traceback
-from distutils.spawn import find_executable
 from typing import Any, Callable, Dict, List, Optional, Tuple, Type, Union
 
 from dmoj.cptbox import IsolateTracer, TracedPopen, syscalls
@@ -413,7 +412,7 @@ def find_command_from_list(cls, files: List[str]) -> Optional[str]:
                 if os.path.exists(file):
                     return file
             else:
-                path = find_executable(file)
+                path = shutil.which(file)
                 if path is not None:
                     return os.path.abspath(path)
         return None

dmoj/executors/shell_executor.py

@@ -1,6 +1,6 @@
 import os
+import shutil
 import sys
-from distutils.spawn import find_executable
 
 from dmoj.executors.script_executor import ScriptExecutor
 
@@ -13,7 +13,7 @@ def get_shell_commands(self):
         return self.shell_commands
 
     def get_allowed_exec(self):
-        return list(map(find_executable, self.get_shell_commands()))
+        return list(map(shutil.which, self.get_shell_commands()))
 
     def get_fs(self):
         return super().get_fs() + self.get_allowed_exec()