### 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
as(limit.child(), EsRelation.class);
    }
    public void testFoldInEval() {
        var plan = optimizedPlan("""
            from test
            | eval a = 1, b = a + 1, c = b + a
            | where c > 10
            """);
        var local = as(plan, LocalRelation.class);
        assertThat(local.supplier(), is(LocalSupplier.EMPTY));
    }
    public void testFoldFromRow() {
        var plan = optimizedPlan("""
              row a = 1, b = 2, c = 3
            | where c > 10
            """);
        as(plan, LocalRelation.class);
    }
    public void testFoldFromRowInEval() {
        var plan = optimizedPlan("""
              row a = 1, b = 2, c = 3
            | eval x = c
            | where x > 10
            """);
        as(plan, LocalRelation.class);
    }
    public void testInvalidFoldDueToReplacement() {
        var plan = optimizedPlan("""
              from test
            | eval x = 1