feat(query-engine): extrapolate rate and increase at boundaries

[milindsrivastava1997]

Summary

• Implement Prometheus boundary extrapolation for counter rate() and increase(), including reset correction, sparse samples, threshold handling, and duration-to-zero clamping.
• Preserve per-key sample counts across accumulator updates, pane merges, JSON, binary (INC7), and Arroyo serialization.
• Thread exact range-vector bounds through instant and range query execution, with per-step range coverage.
• Add focused unit tests and an end-to-end range-query regression test.

Closes #660

Verification

• cargo test -p query_engine_rust
• cargo clippy -p query_engine_rust --all-targets -- -D warnings
• cargo fmt --all -- --check
• git diff --check