feat(precompute): apply spatial filters during ingest routing

[milindsrivastava1997]

Summary

• Compile PromQL spatial filters at precompute startup and runtime config updates.
• Route samples only when both the metric and spatial filter match.
• Reject invalid filters and name matchers before ingest begins.

Tests

• cargo test -p query_engine_rust precompute_engine
• cargo test -p query_engine_rust --test e2e_precompute_equivalence
• cargo test -p query_engine_rust --test e2e_netflow_single_second
• cargo test -p query_engine_rust --test e2e_precompute_wall_clock_fallback_active_ingest