c/sedona-extension: Support PhysicalExpr + try_pushdown_filters() in extension expression / extension exec plan

While we support filter pushdown at the logical level via the TableProvider + Expr, some types of filters are pushed down only at the ExecutionPlan level (e.g., during physical optimization or planning, like for joins that can push down information after seeing both sides of the join). Our file formats internally implement this and use it to calculate a SpatialFilter; however, we don't support this in extension execution plans (but should!).

Start by reading the Sedona extension execution-plan code and the existing file-format handling of PhysicalExpr and try_pushdown_filters(). Compare that path with the logical TableProvider + Expr filter pushdown and its SpatialFilter calculation. Done means extension execution plans support the physical filter-pushdown path used during physical optimization or planning.

Written by the indexing model from the issue text.