load_m1_window collected every bar into an intermediate Vec<M1Parsed> (a full
AoS materialization, un-presized so it grew by reallocation) before transpose_m1
copied it again into the SoA columns — ~2x peak load memory plus realloc churn.
Transpose each chunk straight into the columns instead, via a new shared
M1Columns::extend_from_bars (reserves per chunk for amortized growth). One fewer
full copy, halved peak. Behaviour-preserving: the resulting M1Columns is
byte-identical and transpose_m1's / load_m1_window's signatures are unchanged.
Pinned by a new parity test that needs no live DataServer.
closes#78
Brummel
6390093f93