### 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
from test
            | where emp_no + 1 > 0
            | where salary < 10
            """);
        var optimized = optimizedPlan(plan);
        var topLimit = as(optimized, LimitExec.class);
        var exchange = asRemoteExchange(topLimit.child());
        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 bq = as(source.query(), BoolQueryBuilder.class);
        assertThat(bq.must(), hasSize(2));
        var first = as(sv(bq.must().get(0), "emp_no"), RangeQueryBuilder.class);
        assertThat(first.fieldName(), equalTo("emp_no"));
        assertThat(first.from(), equalTo(-1));
        assertThat(first.includeLower(), equalTo(false));
        assertThat(first.to(), nullValue());
        var second = as(sv(bq.must().get(1), "salary"), RangeQueryBuilder.class);
        assertThat(second.fieldName(), equalTo("salary"));
        assertThat(second.from(), nullValue());
        assertThat(second.to(), equalTo(10));
        assertThat(second.includeUpper(), equalTo(false));
    }
    public void testOnlyPushTranslatableConditionsInFilter() {
        var plan = physicalPlan("""
            from test
            | where round(emp_no) + 1 > 0
            | where salary < 10
            """);