gh-152297: Reify dotted lazy imports with the full dotted name

[Kuhai9801]

Fix lazy reification for dotted imports so lazy import pkg.sub calls __import__ with the full dotted name, matching eager import behavior.

The regression tests cover custom __import__ hooks and first-use loading of the dotted target.

Tests:

• git diff --check
• GitHub Actions required checks after squash

• Issue: Dotted lazy import reification bypasses full-name __import__ hook #152297

[python-cla-bot]

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