### 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 skipPlan(Filter filter) {
            return LogicalPlanOptimizer.skipPlan(filter);
        }
    }
    static class SkipQueryOnLimitZero extends OptimizerRules.SkipQueryOnLimitZero {
        @Override
        protected LogicalPlan skipPlan(Limit limit) {
            return LogicalPlanOptimizer.skipPlan(limit);
        }
    }
    static class PruneEmptyPlans extends OptimizerRules.OptimizerRule<UnaryPlan> {
        @Override
        protected LogicalPlan rule(UnaryPlan plan) {
            return plan.output().isEmpty() ? skipPlan(plan) : plan;
        }
    }
    static class PropagateEmptyRelation extends OptimizerRules.OptimizerRule<UnaryPlan> {
        @Override
        protected LogicalPlan rule(UnaryPlan plan) {
            LogicalPlan p = plan;
            if (plan.child() instanceof LocalRelation local && local.supplier() == LocalSupplier.EMPTY) {