optimize deltalake export memory - #241
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this addresses #237
At a 512 MiB threshold that's ~3.4 GB against the 8 GB limit instead of ~5.3 GB.
shapely WKB decoding — 4.18x on its own. .to_list() built a Python bytes per row and shapely.from_wkb a GEOS geometry per row. Replaced with a numpy reader: PostGIS EWKB points are fixed-width, so the values buffer reshapes directly. Falls back to shapely for anything non-uniform (big-endian, 2D, mixed types).
Per-spec full-table copies. Each of your 4 specs materialised the whole table twice while the shared frame stayed alive. Now the derived columns attach to the decoded batches zero-copy.
The partitioned write — 3.93x. The writer holds an open Parquet writer per partition and flushes only when the call returns. Now written in bounded groups of partitions.
pl.cut materialised a string label per row (categorical→Utf8→Int32). Replaced with np.searchsorted.