[VL] Spark 4.x: CastTransformer does not pass per-expression timezone for timestamp formatting #11918

Backend

VL (Velox)

Bug description

CastTransformer does not pass per-expression timezone through Substrait. When casting timestamp to string, Velox does not use the session timezone, producing output that differs from Spark's expected format.

This is a Substrait architecture limitation that requires changes at the C++ layer.

Affects both Spark 4.0 and 4.1.

Parent issue: #11550

Impact