Range query pipeline drops keys_query and hardcodes is_exact_query=false

[milindsrivastava1997]

execute_range_query_pipeline, used by PromQL range queries (both plain and binary-expr, since the binary-expr range path calls this per arm), has two problems:

1. It never reads keys_query. Dual-population metrics silently lose the keys side over a range, unlike the instant-query path, which handles both keys and values.
2. It unconditionally forces is_exact_query = false regardless of the aggregation's actual WindowType (promql.rs:1144). Sliding-window aggregations are merged incorrectly for every range query as a result.