Move benchmarks into the test directory

[carmocca]

What does this PR do?

Part of #7614

Requested by @Borda in #7614 (review)

Does your PR introduce any breaking changes? If yes, please list them.

None

Before submitting

• Was this discussed/approved via a GitHub issue? (not for typos and docs)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure your PR does only one thing, instead of bundling different changes together?
• [n/a] Did you make sure to update the documentation with your changes? (if necessary)
• [n/a] Did you write any new necessary tests? (not for typos and docs)
• Did you verify new and existing tests pass locally with your changes?
• Did you list all the breaking changes introduced by this pull request?
• [n/a] Did you update the CHANGELOG? (not for typos, docs, test updates, or internal minor changes/refactorings)

PR review

• Is this pull request ready for review? (if not, please submit in draft mode)
• Check that all items from Before submitting are resolved
• Make sure the title is self-explanatory and the description concisely explains the PR
• Add labels and milestones (and optionally projects) to the PR so it can be classified

cc @carmocca @akihironitta @Borda

[github-actions]

Build Error! No Linked Issue found. Please link an issue or mention it in the body using #<issue_id>

[Borda]

pls, share the motivations? I do not see it in the other PR #7614 neither 🐰
also not sure why shall move benchmarks to tests, while benchmarks work as parity testing and then shall be excluded from normal testing...

[carmocca]

pls, share the motivations? I do not see it in the other PR #7614 neither

@Borda the other PR has "fixes" and "closes" linking to issues/PRs that show the motivation.

also not sure why shall move benchmarks to tests, while benchmarks work as parity testing and then shall be excluded from normal testing...

I don't get what you are saying, but the reason it needs to be moved is that the benchmarks depend on many testing components (see the imports in the code), which means that since we will not be distributing them together after #7614, the imports will not work. This is the same reason why the MNIST implementation was copied in #7614, but in this case, moving the directories together instead.

Additionally, these benchmarks are tests in the sense that they are run in our CI and their failure acts as a test failure.