Optimise aggregates active mode pipeline

[pgigis]

Summary

• Improve aggregates active mode behavior and flow fallback logic.
• Fix drop expiration / retransmission accounting and aggregate pending state.
• Improve CLI / daemon reporting and add diagnostics for backpressure and XDP runs.
• Add tests for aggregate and flow evaluation paths.

Testing

• cmake -S . -B build && cmake --build build
• Unit tests (ctest --test-dir build) if available
• Other (describe): git diff --check

Notes

• Aggregate and individual flow results are now reported separately.