[ty] fix stack overflow when comparing recursive NamedTuple types with is_disjoint_from

[mtshiba]

Summary

I found this bug while working on #20528.
The minimum reproducible code is:

from __future__ import annotations

from typing import NamedTuple
from ty_extensions import is_disjoint_from, static_assert

class Path(NamedTuple):
    prev: Path | None
    key: str

static_assert(not is_disjoint_from(Path, Path))

A stack overflow occurs when a nominal instance type inherits from NamedTuple and is defined recursively.
This PR fixes this bug.

Test Plan

mdtest updated

[github-actions]

Diagnostic diff on typing conformance tests

No changes detected when running ty on typing conformance tests ✅

[github-actions]

mypy_primer results

No ecosystem changes detected ✅
No memory usage changes detected ✅

[sharkdp]

Thank you!