roachtest: enforce at-most once remote command execution

Currently, roachtest uses `roachprod.Run` with `DefaultRunOptions` for remote command execution, e.g., running workload(s). The `DefaultRunOptions` include `DefaultRetryOpt`, which performs up to 2 retries; i.e., a specified command may be executed at most 3 times. Many commands are in fact _not_ idempotent. It's probably ok to retry a workload, but only if it fails _cleanly_. In some rare cases, it's possible to end up with _multiple_ concurrent instances, which could lead to corrupted metrics [1], and other unwanted side-effects. We should provide an implementation which enforces _at-most once_ execution, e.g., using systemd.unit, as well as audit existing roachtests.
The implementation might also be in support of the problem described in [2].

[1] https://github.com/cockroachdb/cockroach/issues/142513#issuecomment-2764936630
[2] https://github.com/cockroachdb/cockroach/issues/143455

Jira issue: CRDB-49075