### 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
}
    /**
     * Expected
     * EvalExec[[emp_no{f}#5 * 10[INTEGER] AS emp_no_10]]
     * \_LimitExec[10[INTEGER]]
     *   \_ExchangeExec[]
     *     \_ProjectExec[[_meta_field{f}#11, emp_no{f}#5, first_name{f}#6, !gender, languages{f}#8, last_name{f}#9, salary{f}#10]]
     *       \_FieldExtractExec[_meta_field{f}#11, emp_no{f}#5, first_name{f}#6, !g..]
     *         \_EsQueryExec[test], query[{"range":{"emp_no":{"gt":0,"boost":1.0}}}][_doc{f}#12], limit[10], sort[]
     */
    public void testPushLimitAndFilterToSource() {
        var optimized = optimizedPlan(physicalPlan("""
            from test
            | eval emp_no_10 = emp_no * 10
            | where emp_no > 0
            | limit 10
            """));
        var eval = as(optimized, EvalExec.class);
        var topLimit = as(eval.child(), LimitExec.class);
        var exchange = asRemoteExchange(topLimit.child());
        var project = as(exchange.child(), ProjectExec.class);
        var extract = as(project.child(), FieldExtractExec.class);
        assertThat(
            names(extract.attributesToExtract()),
            contains("_meta_field", "emp_no", "first_name", "gender", "job", "job.raw", "languages", "last_name", "long_noidx", "salary")
        );
        var source = source(extract.child());
        assertThat(source.estimatedRowSize(), equalTo(allFieldRowSize + Integer.BYTES * 2));
        assertThat(source.limit().fold(), is(10));
        var rq = as(sv(source.query(), "emp_no"), RangeQueryBuilder.class);