### 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 project = as(exchange.child(), ProjectExec.class);
        var fieldExtract = as(project.child(), FieldExtractExec.class);
        var source = source(fieldExtract.child());
        assertThat(source.estimatedRowSize(), equalTo(allFieldRowSize + Integer.BYTES));
        var top = as(source.query(), BoolQueryBuilder.class);
        assertThat(top.must(), hasSize(2));
        var first = as(top.must().get(0), BoolQueryBuilder.class);
        var rq = as(sv(first.should().get(0), "emp_no"), RangeQueryBuilder.class);
        assertThat(rq.fieldName(), equalTo("emp_no"));
        assertThat(rq.from(), equalTo(-1));
        assertThat(rq.includeLower(), equalTo(false));
        assertThat(rq.to(), nullValue());
        rq = as(sv(first.should().get(1), "salary"), RangeQueryBuilder.class);
        assertThat(rq.fieldName(), equalTo("salary"));
        assertThat(rq.from(), nullValue());
        assertThat(rq.to(), equalTo(10));
        assertThat(rq.includeUpper(), equalTo(false));
        var second = as(top.must().get(1), BoolQueryBuilder.class);
        rq = as(sv(second.should().get(0), "salary"), RangeQueryBuilder.class);
        assertThat(rq.fieldName(), equalTo("salary"));
        assertThat(rq.from(), nullValue());
        assertThat(rq.to(), equalTo(10000));
        assertThat(rq.includeUpper(), equalTo(true));
        rq = as(sv(second.should().get(1), "salary"), RangeQueryBuilder.class);
        assertThat(rq.fieldName(), equalTo("salary"));
        assertThat(rq.from(), equalTo(50000));
        assertThat(rq.includeLower(), equalTo(true));
        assertThat(rq.to(), nullValue());
    }
    public void testLimit() {