Count underlying requests in synced rollups

[starkdmi]

Summary

• Count the underlying requests recorded in each usage event when building synced provider and model rollups. One stored event may aggregate multiple API requests.
• Use the same request count in the local today/week snapshot.
• Advance the sync rollup version so existing rollups are rebuilt and sent again on the next sync.

Cause

The rollup incremented requests once per stored event, even when event.usage.requests recorded multiple requests. The regression test uses synthetic fixtures to cover this case and the one-request fallback.

Verification

• Regression tests pass with synthetic fixtures.
• cargo test -p statsai-store
• cargo clippy -p statsai-store --all-targets -- -D warnings
• cargo clippy -p statsai-daemon --features watch --all-targets -- -D warnings
• ./scripts/rust-ci.sh full
• GitHub CI checks passed.