promql.rs: range-context arithmetic duplicated between usual and binary-expr range paths

[milindsrivastava1997]

`build_arm_range_context` (case: range/binary-expr, `engines/simple_engine/promql.rs`) and `build_range_query_execution_context_from_parsed` (case: range/usual, same file) are line-for-line identical from the point each has a base `QueryExecutionContext`