### 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
assertThat(rq.fieldName(), equalTo("emp_no"));
        assertThat(rq.from(), equalTo(0));
        assertThat(rq.includeLower(), equalTo(false));
        assertThat(rq.to(), nullValue());
    }
    /**
     * Expected
     * TopNExec[[Order[emp_no{f}#2,ASC,LAST]],1[INTEGER]]
     * \_LimitExec[1[INTEGER]]
     *   \_ExchangeExec[]
     *     \_ProjectExec[[_meta_field{f}#8, emp_no{f}#2, first_name{f}#3, !gender, languages{f}#5, last_name{f}#6, salary{f}#7]]
     *       \_FieldExtractExec[_meta_field{f}#8, emp_no{f}#2, first_name{f}#3, !ge..]
     *         \_EsQueryExec[test], query[][_doc{f}#9], limit[1], sort[]
     */
    public void testQueryWithLimitSort() throws Exception {
        var optimized = optimizedPlan(physicalPlan("""
            from test
            | limit 1
            | sort emp_no
            """));
        var topN = as(optimized, TopNExec.class);
        var limit = as(topN.child(), LimitExec.class);
        var exchange = asRemoteExchange(limit.child());
        var project = as(exchange.child(), ProjectExec.class);
        var extract = as(project.child(), FieldExtractExec.class);
        var source = source(extract.child());
        assertThat(source.estimatedRowSize(), equalTo(allFieldRowSize + Integer.BYTES));
    }
    /**
     * Expected