fix: vertex.edges() and graph.edges() return a new container, not the internal one

[petercorke]

Summary

vertex.edges() and graph.edges() returned the object's own edge list/set, so a caller could corrupt the graph without meaning to:

b.edges().clear()        # empties b's edge list ...
g.ne                     # ... but the graph still counts the edges

and removing edges while iterating v.edges() skipped some, because remove_edge mutates the list being iterated. Both now return a new container (list / set), so a caller can do what it likes with the result.

Audit first

Nothing relied on the aliasing:

• inside pgraph the only consumer of vertex.edges() is degree (len() only);
• every call site in RTB (PoseGraph, LatticePlanner), MVTB and spatialmath only iterates the result or takes its length; none mutates it.

Cost

graph.edges() on a 3,000-edge graph is about 9 µs per call; vertex.edges() is about 0.05 µs.

Docs

The BaseVertex.edges() :return: said "edges leaving this vertex" for both graph kinds, which is wrong for an undirected graph (it lists incident edges). The docstring now states which edges are returned for each kind, that an undirected self-loop is listed twice (once per end, the same reason it counts 2 towards the degree), and that the result is a copy.

Tests

tests/test_edges_copy.py, 24 tests across UGraph and DGraph (16 fail on main): type, not the internal object, new object per call, clearing/appending to the result leaves the graph intact, removing while iterating is safe, contents and self-loop listing per graph kind. Full suite 239 passing, mypy and pyflakes clean.

🤖 Generated with Claude Code

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

View in Codacy

🟢 Metrics 17 complexity · 3 duplication

Metric	Results
Complexity	17
Duplication	3

View in Codacy

_{NEW Get contextual insights on your PRs based on Codacy's metrics, along with PR and Jira context, without leaving GitHub. Enable AI reviewer
TIP This summary will be updated as you push new changes.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.36%. Comparing base (d22408d) to head (9d89f01).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #36      +/-   ##
==========================================
+ Coverage   93.27%   93.36%   +0.09%     
==========================================
  Files           3        3              
  Lines        1055     1055              
==========================================
+ Hits          984      985       +1     
+ Misses         71       70       -1     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[petercorke]

Superseded by #43 (graph.edges() is now an ordered list, and both edges() methods return copies), which also covers this PR's vertex-side docstring correction and tests. Closing in favour of that.