Fix findCycles missing self-loops created with named edges

[chatman-media]

Fixes #111.

findCycles decides whether a single-node strongly-connected component is a cycle by calling graph.hasEdge(v, v). That overload only matches the default (unnamed) edge, so a self-loop added as a named edge in a multigraph (setEdge(v, v, label, name)) is missed and the node is wrongly reported as cycle-free.

Switched the check to graph.outEdges(v, v), which returns every edge between v and itself regardless of name, so any self-loop is detected. Behaviour for unnamed self-loops is unchanged.

Repro (before this PR returns []):

const g = new Graph({ multigraph: true });
g.setEdge('a', 'a', 'label', 'name');
findCycles(g); // expected [['a']]

Added a regression test (fails without the fix). Full suite (256 tests), typecheck and lint all pass.