### 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/LogicalPlanOptimizerTests.java
assertTrue(lt.left() instanceof ReferenceAttribute);
        var refAttr = (ReferenceAttribute) lt.left();
        assertEquals("x", refAttr.name());
        assertEquals(L(7), lt.right());
        var eval = as(filter.child(), Eval.class);
        assertEquals(1, eval.fields().size());
        assertTrue(eval.fields().get(0) instanceof Alias);
        assertEquals("x", (eval.fields().get(0)).name());
        filter = as(eval.child(), Filter.class);
        assertTrue(filter.condition() instanceof And);
        var and = (And) filter.condition();
        assertTrue(and.left() instanceof GreaterThan);
        var gt = (GreaterThan) and.left();
        assertTrue(gt.left() instanceof FieldAttribute);
        assertEquals("emp_no", ((FieldAttribute) gt.left()).name());
        assertTrue(and.right() instanceof LessThan);
        lt = (LessThan) and.right();
        assertTrue(lt.left() instanceof FieldAttribute);
        assertEquals("emp_no", ((FieldAttribute) lt.left()).name());
        assertTrue(filter.child() instanceof EsRelation);
    }
    public void testNoPushDownOrFilterPastLimit() {
        LogicalPlan plan = optimizedPlan("""
            from test
            | limit 3
            | where emp_no < 3 or salary > 9""");
        var limit = as(plan, Limit.class);
        var filter = as(limit.child(), Filter.class);
        assertTrue(filter.condition() instanceof Or);
        var or = (Or) filter.condition();