Promote timing tests in internal/aggregated/storage still flake under host load #354

Summary

The promote timing tests in internal/aggregated/storage still flake under host load, after #309 (which fixed #288):

• TestTemplatePromoteConfirmation/timeout_before_apply
• TestTemplatePromoteDeadline/...

Both failed together in one make test run on the PR branch for #352, at a host load average of about 50, and passed on the next run of the same head. #352 does not touch that package.

#288's residual note named the elapsed > 1s wall-clock check in TestTemplatePromoteConfirmation as the likely remaining cause.

Fix

Replace the wall-clock checks with the fake clock or a deterministic hook, as #309 did for the PATCH timing. Run the package with -count=20 under load (for example with stress or a parallel go test of another package) to show it holds.

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