chore: improve Meshroom maintenance path

[lphuc2250gma]

Summary:

• Add or tighten focused edge-case tests or type assertions in tests/utils.py, tests/test_graph.py related to Python typing, tests, CLI ergonomics, observability; avoid docs-only changes and broad refactors.
• Keep the change narrow so it is straightforward to review.

Notes:

• I kept this scoped to the relevant implementation and tests.

[gemini-code-assist]

Code Review

This pull request adds a new test case for empty graphs in tests/test_graph.py and updates type hints in tests/utils.py to use type[desc.Node] instead of desc.Node. A review comment points out that comparing graph.nodes (a DictModel instance) directly to an empty list [] in the new test will fail, and suggests asserting its length instead.

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[gemini-code-assist]

Comparing graph.nodes (which is a DictModel instance) directly to a list [] will evaluate to False because DictModel is a custom container class and not a standard Python list. To check if the graph has no nodes, you should check its length or use its truthiness.

Suggested change

	assert graph.nodes == []
	assert len(graph.nodes) == 0