fix(ls): restore 100% coverage on latest after #9626 (#9646)

Restores the global 100% coverage gate on `latest`, which broke after
#9626.

`filterLinkedStrategyEdges` in `lib/commands/ls.js` skips dev edges on
non-root packages — a guard added in #9095 to suppress false `UNMET
DEPENDENCY` output in the linked strategy. #9626 fixed the root cause
for store packages (they no longer load `devDependencies` as required
edges), so the store-based test no longer produces a dev edge, leaving
that branch unexercised.

Rather than ignore the line, this adds a regression test that genuinely
exercises the guard: arborist still loads dev edges for a `file:`-linked
transitive package, so listing one with `--all` under the linked
strategy reaches the guard at depth > 0 and confirms its devDependency
is suppressed instead of reported as `UNMET DEPENDENCY`. The full test
suite passes at 100%.

This is the `latest` counterpart of #9636, which restored coverage on
`release/v11` via an `istanbul ignore`.

## References

Follows up #9626