### Description

Evals that introduce aliased can be simplified by extracting them into a project (and thus signaling there's no underlying processing).

The following eval:
`eval x = a + 1, y = x, z = y + 1, y = z, w = y + 1`
can be converted into:
`eval x = a + 1, z = a + 1 + 1, w = a + 1 + 1 | project x, z, z as y, w`

This helps fuse the project with other projections/aggs downstream.
x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/LogicalPlanOptimizer.java
@Override
        protected LogicalPlan rule(OrderBy orderBy) {
            LogicalPlan child = orderBy.child();
            if (child instanceof OrderBy childOrder) {
                
                return new OrderBy(orderBy.source(), childOrder.child(), CollectionUtils.combine(orderBy.order(), childOrder.order()));
            } else if (child instanceof Project) {
                return pushDownPastProject(orderBy);
            }
            return orderBy;
        }
    }
    /**
     * Remove unused columns created in the plan, in fields inside eval or aggregations inside stats.
     */
    static class PruneColumns extends Rule<LogicalPlan, LogicalPlan> {
        @Override
        public LogicalPlan apply(LogicalPlan plan) {
            var used = new AttributeSet();
            
            var seenProjection = new Holder<>(Boolean.FALSE);
            
            
            var pl = plan.transformDown(p -> {
                
                if (p instanceof Limit) {
                    return p;