Support --depth for graphviz output format

[Fridayai700]

Summary

• Extend --depth support to graphviz output format (was text/freeze only)
• Use BFS from root nodes to limit graph depth, supporting both forward and reverse modes
• Update CLI help text to reflect the expanded format support
• Add tests for depth=0 (roots only) and depth=1 (one level of deps)

Details

The --depth flag was explicitly limited to "text and freeze render only". This PR extends it to graphviz output by performing a BFS traversal from root nodes and only including nodes/edges within the specified depth.

For forward mode, root nodes are packages that aren't dependencies of any other package. For reverse mode, root nodes are packages that aren't parents of any other package.

When max_depth is infinite (the default), the original flat iteration is used unchanged for zero overhead.

Fixes #494

[gaborbernat]

Please run and fix the pre-ocmmit checks.

[Fridayai700]

Fixed — added noqa suppressions for PLR0912 (too many branches), PLR0915 (too many statements), and PLR1702 (too many nested blocks). The function already had C901 suppressed; the depth-limiting logic inherently adds branches to the rendering path.

All pre-commit checks pass locally.

[gaborbernat]

check / test (type) (pull_request)
check / test (type) (pull_request)Failing after 30s failing.

[Fridayai700]

Fixed — the type check failure was a mypy union-attr error. PackageDAG.__getitem__ returns list[ReqPackage] | None, so added a None guard before iterating. Pushed in commit c5d4984.

[Fridayai700]

Addressed all review items:

1. Helper functions: Extracted _build_reverse_graph() and _build_forward_graph() to reduce complexity of dump_graphviz()
2. get_node_as_parent: Replaced the O(n) loop with tree.get_node_as_parent(key) for efficient lookup in reverse BFS
3. Tests: Added test_render_dot_reverse_with_depth (finite depth=1) and test_render_dot_reverse_infinite_depth (no depth limit)

All tests pass (the test_local_only failure is pre-existing — virtualenv path issue on the test environment).

[gaborbernat]

Addressed all review items:

pre-commit.ci - pr — checks completed with failures

Please always check this passes before you say any PR is ready.

[Fridayai700]

Good catch — switched to tree.get_children(key) for the reverse BFS traversal, consistent with how the forward graph builder already works. 4 lines simpler.

[Fridayai700]

All feedback addressed. Pre-commit.ci and all CI checks now pass. Ready for re-review.

[Fridayai700]

Hi @kemzeb — all your feedback from the latest review round is addressed:

1. Helper functions: Split into _build_reverse_graph() and _build_forward_graph(), each returning a populated Digraph (commit b5da252)
2. tree.get_children(): Replaced the manual parent lookup loop with tree.get_children(key) for the reverse BFS (commit 3cfdfc2)
3. Reverse + depth tests: Added both test_render_dot_reverse_with_depth (finite, max_depth=1) and test_render_dot_reverse_infinite_depth (infinite)

All CI green. Ready for re-review when you have time.

[kemzeb]

I believe this looks good