feature-benchmark: Increase scale of fast scenarios, reduce retries

[def-]

For context see https://materializeinc.slack.com/archives/C0761MZ3QD9/p1732280715336919

Successful nightly: https://buildkite.com/materialize/nightly/builds/10501
Release qualification with known regression: https://buildkite.com/materialize/release-qualification/builds/688

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.

[teskje]

I approve the idea! Not familiar enough with the feature benchmarks to say if this behaves as advertised (in particular I don't see where the number of retries is reduced), but if it passes the Nightlies I assume it must be fine.

[teskje]

Is that change here intentional?

[def-]

Nope, I find submodules to be very annoying. Will fix.