### 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
transientEval.add(aliased);
                    }
                    
                    else {
                        newAggs.add((NamedExpression) agg.replaceChildren(Collections.singletonList(s)));
                    }
                } else {
                    newAggs.add(agg);
                }
            }
            LogicalPlan plan = aggregate;
            if (changed) {
                var source = aggregate.source();
                plan = new Aggregate(aggregate.source(), aggregate.child(), aggregate.groupings(), newAggs);
                
                if (transientEval.size() > 0) {
                    plan = new Eval(source, plan, transientEval);
                    
                    
                    
                    plan = new EsqlProject(source, plan, Expressions.asAttributes(aggs));
                }
            }
            return plan;
        }
        private static String temporaryName(NamedExpression agg, AggregateFunction af) {
            return "__" + agg.name() + "_" + af.functionName() + "@" + Integer.toHexString(af.hashCode());
        }
    }
    static class ConvertStringToByteRef extends OptimizerRules.OptimizerExpressionRule<Literal> {