### 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/PhysicalPlanOptimizerTests.java
""");
        var optimized = optimizedPlan(plan);
        var limit = as(optimized, LimitExec.class);
        var aggregateFinal = as(limit.child(), AggregateExec.class);
        assertThat(aggregateFinal.estimatedRowSize(), equalTo(Long.BYTES));
        var aggregatePartial = as(aggregateFinal.child(), AggregateExec.class);
        var filter = as(aggregatePartial.child(), FilterExec.class);
        var topN = as(filter.child(), TopNExec.class);
        var exchange = asRemoteExchange(topN.child());
        var project = as(exchange.child(), ProjectExec.class);
        var extract = as(project.child(), FieldExtractExec.class);
        assertThat(names(extract.attributesToExtract()), contains("salary", "emp_no", "last_name"));
        var source = source(extract.child());
        assertThat(source.limit(), is(topN.limit()));
        assertThat(source.sorts(), is(sorts(topN.order())));
        assertThat(source.limit(), is(l(10)));
        assertThat(source.sorts().size(), is(1));
        FieldSort order = source.sorts().get(0);
        assertThat(order.direction(), is(ASC));
        assertThat(name(order.field()), is("last_name"));
        
        int estimatedSize = KEYWORD_EST + Integer.BYTES * 6;
        assertThat(source.estimatedRowSize(), equalTo(estimatedSize));
    }
    /**
     * Expected
     * EvalExec[[emp_no{f}#7 + 1[INTEGER] AS e, emp_no{f}#7 + 1[INTEGER] AS emp_no]]
     * \_LimitExec[10000[INTEGER]]
     *   \_ExchangeExec[[],false]
     *     \_ProjectExec[[_meta_field{f}#13, emp_no{f}#7, first_name{f}#8, gender{f}#9, job{f}#14, job.raw{f}#15, languages{f}#10, last