Incorrect diagnostic on missing submodule

Bug Report

When untyped module exists but submodule does not, mypy reports that submodule is installed.

To Reproduce

$ pip install fabric

import fabric
from fabric.not_exists import something

$ python3 test.py
Traceback (most recent call last):
  File "/media/sf_d/WWPass/git/spm/test.py", line 2, in <module>
    from fabric.not_exists import something
ModuleNotFoundError: No module named 'fabric.not_exists'

$ mypy test.py
test.py:1:1: error: Skipping analyzing "fabric": module is installed, but missing library stubs or py.typed marker  [import-untyped]
    import fabric
    ^
test.py:2:1: error: Skipping analyzing "fabric.not_exists": module is installed, but missing library stubs or py.typed marker  [import-untyped]
    from fabric.not_exists import something
    ^
test.py:2:1: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports
Found 2 errors in 1 file (checked 1 source file)

Expected Behavior
Error in line 2 should be saying that fabric.not_exists does not exist.

Actual Behavior
Error in line 2 says that fabric.not_exists is installed, which it not true and misleading.

Your Environment

$ mypy --version
mypy 1.11.2 (compiled: yes)

$ python3 --version
Python 3.12.3

$ pip list | grep fabric
fabric 3.2.2

示されている test.py、インストール済みの型付けされていない fabric パッケージ、そして fabric.not_exists のインポートを使って報告を再現してください。まず、mypy のインポート解決と、ネストされたモジュールに対するスタブ欠落の診断を追跡します。既存のパッケージが現在の警告を引き続き報告し、一方で存在しないサブモジュールには明確な does-not-exist エラーが出れば完了です。