### 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/test/java/org/elasticsearch/xpack/esql/optimizer/LocalPhysicalPlanOptimizerTests.java
package org.elasticsearch.xpack.esql.optimizer;
import com.carrotsearch.randomizedtesting.annotations.ParametersFactory;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.core.Tuple;
import org.elasticsearch.index.query.QueryBuilder;
import org.elasticsearch.index.query.QueryBuilders;
import org.elasticsearch.test.ESTestCase;
import org.elasticsearch.xpack.core.enrich.EnrichPolicy;
import org.elasticsearch.xpack.esql.EsqlTestUtils;
import org.elasticsearch.xpack.esql.analysis.Analyzer;
import org.elasticsearch.xpack.esql.analysis.AnalyzerContext;
import org.elasticsearch.xpack.esql.analysis.EnrichResolution;
import org.elasticsearch.xpack.esql.analysis.Verifier;
import org.elasticsearch.xpack.esql.enrich.EnrichPolicyResolution;
import org.elasticsearch.xpack.esql.expression.function.EsqlFunctionRegistry;
import org.elasticsearch.xpack.esql.parser.EsqlParser;
import org.elasticsearch.xpack.esql.plan.physical.AggregateExec;
import org.elasticsearch.xpack.esql.plan.physical.EsQueryExec;
import org.elasticsearch.xpack.esql.plan.physical.EsStatsQueryExec;
import org.elasticsearch.xpack.esql.plan.physical.EsStatsQueryExec.Stat;
import org.elasticsearch.xpack.esql.plan.physical.EstimatesRowSize;
import org.elasticsearch.xpack.esql.plan.physical.EvalExec;
import org.elasticsearch.xpack.esql.plan.physical.ExchangeExec;
import org.elasticsearch.xpack.esql.plan.physical.LimitExec;
import org.elasticsearch.xpack.esql.plan.physical.PhysicalPlan;
import org.elasticsearch.xpack.esql.planner.FilterTests;
import org.elasticsearch.xpack.esql.planner.Mapper;
import org.elasticsearch.xpack.esql.planner.PlannerUtils;
import org.elasticsearch.xpack.esql.plugin.QueryPragmas;
import org.elasticsearch.xpack.esql.session.EsqlConfiguration;