[3.14] gh-134466: Don't run when termios is inaccessible (GH-138911) (GH-139029)

Without the ability to set required capabilities, the REPL cannot
function properly (syntax highlighting and multiline editing can't
work).
We refuse to work in this degraded state.

(cherry picked from commit 2fc7004d54)

Co-authored-by: Łukasz Langa <lukasz@langa.pl>

Lib/_pyrepl/fancy_termios.py

@@ -20,19 +20,25 @@
 import termios
 
 
-class TermState:
-    def __init__(self, tuples):
-        (
-            self.iflag,
-            self.oflag,
-            self.cflag,
-            self.lflag,
-            self.ispeed,
-            self.ospeed,
-            self.cc,
-        ) = tuples
+TYPE_CHECKING = False
 
-    def as_list(self):
+if TYPE_CHECKING:
+    from typing import cast
+else:
+    cast = lambda typ, val: val
+
+
+class TermState:
+    def __init__(self, attrs: list[int | list[bytes]]) -> None:
+        self.iflag = cast(int, attrs[0])
+        self.oflag = cast(int, attrs[1])
+        self.cflag = cast(int, attrs[2])
+        self.lflag = cast(int, attrs[3])
+        self.ispeed = cast(int, attrs[4])
+        self.ospeed = cast(int, attrs[5])
+        self.cc = cast(list[bytes], attrs[6])
+
+    def as_list(self) -> list[int | list[bytes]]:
         return [
             self.iflag,
             self.oflag,
@@ -45,32 +51,32 @@ def as_list(self):
             self.cc[:],
         ]
 
-    def copy(self):
+    def copy(self) -> "TermState":
         return self.__class__(self.as_list())
 
 
-def tcgetattr(fd):
+def tcgetattr(fd: int) -> TermState:
     return TermState(termios.tcgetattr(fd))
 
 
-def tcsetattr(fd, when, attrs):
+def tcsetattr(fd: int, when: int, attrs: TermState) -> None:
     termios.tcsetattr(fd, when, attrs.as_list())
 
 
 class Term(TermState):
     TS__init__ = TermState.__init__
 
-    def __init__(self, fd=0):
+    def __init__(self, fd: int = 0) -> None:
         self.TS__init__(termios.tcgetattr(fd))
         self.fd = fd
-        self.stack = []
+        self.stack: list[list[int | list[bytes]]] = []
 
-    def save(self):
+    def save(self) -> None:
         self.stack.append(self.as_list())
 
-    def set(self, when=termios.TCSANOW):
+    def set(self, when: int = termios.TCSANOW) -> None:
         termios.tcsetattr(self.fd, when, self.as_list())
 
-    def restore(self):
+    def restore(self) -> None:
         self.TS__init__(self.stack.pop())
         self.set()