### 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
);
        analyzer = new Analyzer(new AnalyzerContext(config, functionRegistry, getIndexResult, enrichResolution), TEST_VERIFIER);
    }
    public void testSingleFieldExtractor() {
        
        
        var plan = physicalPlan("""
            from test
            | where round(emp_no) > 10
            """);
        var optimized = optimizedPlan(plan);
        var topLimit = as(optimized, LimitExec.class);
        var exchange = asRemoteExchange(topLimit.child());
        var project = as(exchange.child(), ProjectExec.class);
        var restExtract = as(project.child(), FieldExtractExec.class);
        var limit = as(restExtract.child(), LimitExec.class);
        var filter = as(limit.child(), FilterExec.class);
        var extract = as(filter.child(), FieldExtractExec.class);
        assertEquals(Sets.difference(allFields(mapping), Set.of("emp_no")), Sets.newHashSet(names(restExtract.attributesToExtract())));
        assertEquals(Set.of("emp_no"), Sets.newHashSet(names(extract.attributesToExtract())));
        var query = as(extract.child(), EsQueryExec.class);
        assertThat(query.estimatedRowSize(), equalTo(Integer.BYTES + allFieldRowSize));
    }
    private Set<String> allFields(Map<String, EsField> mapping) {
        Set<String> result = new HashSet<>();
        for (Map.Entry<String, EsField> entry : mapping.entrySet()) {
            String key = entry.getKey();
            result.add(key);
            for (Map.Entry<String, EsField> sub : entry.getValue().getProperties().entrySet()) {
                result.add(key + "." + sub.getKey());