refactor(client): drop unread total_success snapshot field

[staging-devin-ai-integration]

Summary

• MetricsSnapshot.total_success had no reader — it was kept alive only by a rationale-free #[allow(dead_code)], which silently disabled dead-code checking for the whole struct.
• Dropped the field; the derived values operators actually see (total_failures, success_rate) are still computed from the same local counter in get_snapshot, so printed output is unchanged.

Review & Validation

• Confirm nothing outside apps/skit-cli/src/load_test/ consumed the field (repo-wide grep shows only in-module construction).
• cargo clippy -p streamkit-client --all-targets and cargo test -p streamkit-client pass locally.

Link to Devin session: https://staging.itsdev.in/sessions/2345b1cb7fee4f8491cf0f5659aac0ab
Open in Devin Desktop: https://staging.itsdev.in/desktop/session/2345b1cb7fee4f8491cf0f5659aac0ab?variant=devin-insiders
Requested by: @streamer45

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Devin Review

Status	Commit
🟢 Reviewed	261d1d5

[staging-devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring

[staging-devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

Debug

Playground