The six intrinsic pf_argsort specifics, their key extraction, and the engine dispatch.
This is the argsort tier's implementation, and what it does NOT reach is the point. Nothing
here names parquet_bindings: the C++ engine is reached through the procedure pointers
parquet_argsort holds, which parquet_sorting_oracle binds and which a program that never
imports that module never has bound. See parquet_argsort's own header.
This file decides nothing about order. It extracts values, says which rows are null, and
passes the caller's descending/nulls_first flags through -- every ordering decision is made
in sort_compare_key (src/parquet_argsort_engine.f90), which is what stops a raw-array sort, a
table sort and a read-time sort_by= from ever disagreeing.