gh-125843: indicate which C function caused a curses.error (#125844)

- Rename error helpers with a `curses_set_error_*` prefix instead of `PyCurses*`.
- Cleanly report both NULL and ERR cases.
- Raise `curses.error` in `is_linetouched` instead of a `TypeError`.

Lib/test/test_curses.py

@@ -130,6 +130,9 @@ def test_use_env(self):
         curses.use_env(False)
         curses.use_env(True)
 
+    def test_error(self):
+        self.assertIsSubclass(curses.error, Exception)
+
     def test_create_windows(self):
         win = curses.newwin(5, 10)
         self.assertEqual(win.getbegyx(), (0, 0))