fix(gfql/row): close #1373 cuDF host bridge + row test follow-ups

[lmeyerov]

Summary

Closes the remaining Worker C follow-ups for #1373 by hardening the ORDER BY stringified-list path and continuing row-test placement cleanup.

What changed

• Added a defensive cuDF host-bridge in graphistry/compute/gfql/row/pipeline.py for parsed stringified-list sort keys before assign(...) when a pandas Series is present.
• Clarified caller contract in parse_stringified_list_series() docstring (graphistry/compute/gfql/row/ordering.py).
• Added row-level regression in graphistry/tests/compute/gfql/row/test_ordering.py for stringified-list subscript ORDER BY expressions.
• Removed two row-heavy cypher-layer duplicates from graphistry/tests/compute/gfql/cypher/test_lowering.py while keeping thin cypher smoke coverage.
• Added changelog entry under Development.

Why

• Prevent latent cuDF host mismatch regressions if parsed sort keys materialize as pandas Series.
• Keep row-pipeline semantics tested at the row layer, reducing unnecessary cypher-parser coupling.

Validation

• python -m pytest -q graphistry/tests/compute/gfql/row/test_ordering.py
• python -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py -k "stringified_list_column_uses_list_orderability or order_by_list_literal_and_subscript_expression or order_by_stringified_list_subscript_expression"
• python -m pytest -q graphistry/tests/compute/gfql/test_row_pipeline_ops.py -k "order_by_stringified_list_column_on_cudf_when_available or order_by_stringified_list_column_uses_list_orderability"
• uv run ruff check graphistry/compute/gfql/row/pipeline.py graphistry/compute/gfql/row/ordering.py graphistry/tests/compute/gfql/row/test_ordering.py graphistry/tests/compute/gfql/cypher/test_lowering.py
• ./bin/mypy.sh graphistry/compute/gfql/row/pipeline.py graphistry/compute/gfql/row/ordering.py

Links

• Issue: GFQL row pipeline: cuDF host-bridge gap in order_by + test placement debt for compute/gfql/row/ (follow-ups from #1362/#1359) #1373
• Meta: [FEA] GFQL bindings_table (row bindings) from chain using Yannakakis prune #880