fix: avoid swallowing sample document cache errors

[jmolz]

Fixes #869.

Summary

• Replace the bare except around os.mkdir("doc-cache") with os.makedirs(..., exist_ok=True).
• Remove an unused import and keep request adapter imports at module import scope so the touched file passes Ruff.

Tests

• python3 -m py_compile trustgraph-cli/trustgraph/cli/load_sample_documents.py
• ruff check trustgraph-cli/trustgraph/cli/load_sample_documents.py
• git diff --check

[github-actions]

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[cybermaggedon]

Thanks for the fix!

[jmolz]

Thanks for the fix!

My pleasure!