Fix LMS crash

[ashman-p]

HSS signing operation crashed after exhausting the number of signatures available at a given level.
The multi-level tree was not properly populated.

Fixes #1966.

• Does this PR change the input/output behaviour of a cryptographic algorithm (i.e., does it change known answer test values)? (If so, a version bump will be required from x.y.z to x.(y+1).0.)
• Does this PR change the list of algorithms available -- either adding, removing, or renaming? Does this PR otherwise change an API? (If so, PRs in fully supported downstream projects dependent on these, i.e., oqs-provider will also need to be ready for review and merge by the time this is merged.)

[SWilson4]

Thanks for the fix, @ashman-p. Would it be feasible to add a test that catches the original bug to prevent a regression and catch similar errors that may arise in the future? Something that fails on the current main but passes on this branch. I can help with integrating it into CI.

[ashman-p]

Thanks for the fix, @ashman-p. Would it be feasible to add a test that catches the original bug to prevent a regression and catch similar errors that may arise in the future? Something that fails on the current main but passes on this branch. I can help with integrating it into CI.

Thanks @SWilson4 . I thought about that and wondered if this speed test would suffice? IOW invoking a small HSS and LMS variant?

[SWilson4]

Thanks @SWilson4 . I thought about that and wondered if this speed test would suffice? IOW invoking a small HSS and LMS variant?

I think that would do the trick. Would it be more of a stress test? If so, maybe we can add it to the extended tests so it only runs once a week or on-demand. If that makes sense, how about I push a commit to this branch to add the CI framework, and then you can refine it as need be?

[ashman-p]

Thanks @SWilson4 . I thought about that and wondered if this speed test would suffice? IOW invoking a small HSS and LMS variant?

I think that would do the trick. Would it be more of a stress test? If so, maybe we can add it to the extended tests so it only runs once a week or on-demand. If that makes sense, how about I push a commit to this branch to add the CI framework, and then you can refine it as need be?

I am not sure this particular test needs to be a stress test. Seems that the duration and number of iterations are configurable.
Therefore, the options can be selected to really make it a sanity test rather than a stressor. And it can cover LMS and XMSS.
Please push the branch to the CI framework and maybe give me some instructions about what to do next? Thanks