### 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
*          \_EsQueryExec[test], query[sv(emp_no, not(emp_no == 10010)) OR sv(not(first_name == "Parto"))], limit[10000], sort[]
     */
    public void testPushDownNegatedConjunction() {
        var plan = physicalPlan("""
            from test
            | where not (emp_no == 10010 and first_name == "Parto")
            """);
        var optimized = optimizedPlan(plan);
        var topLimit = as(optimized, LimitExec.class);
        var exchange = asRemoteExchange(topLimit.child());
        var project = as(exchange.child(), ProjectExec.class);
        var extractRest = as(project.child(), FieldExtractExec.class);
        var source = source(extractRest.child());
        assertThat(source.estimatedRowSize(), equalTo(allFieldRowSize + Integer.BYTES));
        var bq = as(source.query(), BoolQueryBuilder.class);
        assertThat(bq.should(), hasSize(2));
        var empNo = as(sv(bq.should().get(0), "emp_no"), BoolQueryBuilder.class);
        assertThat(empNo.mustNot(), hasSize(1));
        var tq = as(empNo.mustNot().get(0), TermQueryBuilder.class);
        assertThat(tq.fieldName(), equalTo("emp_no"));
        assertThat(tq.value(), equalTo(10010));
        var firstName = as(sv(bq.should().get(1), "first_name"), BoolQueryBuilder.class);
        assertThat(firstName.mustNot(), hasSize(1));
        tq = as(firstName.mustNot().get(0), TermQueryBuilder.class);
        assertThat(tq.fieldName(), equalTo("first_name"));
        assertThat(tq.value(), equalTo("Parto"));
    }
    /**
     * Expected:
     *  LimitExec[10000[INTEGER]]