fix(sources): catch FileNotFoundError for broken symlinks

[andre-motta]

Closes: #1082

Pull Request Description

What

Add FileNotFoundError to the except clause in scan_compiled_extensions and add a regression test.

Why

Broken symlinks (e.g. .dockerignore → missing .gitignore in PyTorch tarballs) crash the bootstrap with FileNotFoundError since 0.80.0.

• PR follows CONTRIBUTING.md guidelines

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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Run ID: b9764f50-df48-4b8a-bd93-999c48aed831

📥 Commits

Reviewing files that changed from the base of the PR and between 172b371 and 9589c5b.

📒 Files selected for processing (2)

• src/fromager/sources.py
• tests/test_sources.py

✅ Files skipped from review due to trivial changes (2)

• tests/test_sources.py
• src/fromager/sources.py

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📝 Walkthrough

Walkthrough

The PR updates scan_compiled_extensions to catch FileNotFoundError in addition to IsADirectoryError when opening files, so broken symlinks are skipped instead of raising. An accompanying unit test adds a broken-symlink scenario and verifies the function returns no matches rather than raising an error.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main change: catching FileNotFoundError for broken symlinks in the sources module.
Description check	✅ Passed	The description is directly related to the changeset, explaining what was added (FileNotFoundError handling and regression test) and why (broken symlinks cause crashes).
Linked Issues check	✅ Passed	The PR fully addresses the requirements from #1082: it catches FileNotFoundError in scan_compiled_extensions and adds a regression test for broken symlinks.
Out of Scope Changes check	✅ Passed	All changes are directly related to fixing the broken symlink handling issue; no unrelated modifications are present.

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[LalatenduMohanty]

@mergify rebase

[mergify]

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