Split cannon benchmarks and tests

[pcapriotti]

Cannon benchmarks were running as part of the test suite. This creates a separate component for cannon benchmarks, so that they are not run alonside the other unit tests.

Checklist

• The PR Title explains the impact of the change.
• The PR description provides context as to why the change should occur and what the code contributes to that effect. This could also be a link to a JIRA ticket or a Github issue, if there is one.
• changelog.d contains the following bits of information (details):
  • A file with the changelog entry in one or more suitable sub-sections. The sub-sections are marked by directories inside changelog.d.

[supersven]

Looks good to me. 👍

Let's wait for the CI results. When they're positive, I'll approve.