PgSelect step is not deduplicating

### Summary

When doing `xByRowId` queries with the same constant ID, pgSelect step does not seem to correctly deduplicate


### Steps to reproduce

Setup Postgraphile v5. Add a table with the ability to do a root query to fetch a single row of that table by its row ID

```sql
create table foo (id int primary key, a text);
```

Set `graphile.explain` to `true` in your preset

Execute a query in Ruru using aliases to query the same row twice. e.g.

```gql
query MyFoos {
foo1: foo(id="1") {
id
}
foo2: foo(id="1") {
id
}
}
```

See the diagram of the plan is similar to the screenshot above

Please let me know if it would be useful to create a minimal repro of this. I'm happy to do so

### Expected results

I expect there to be a single PgSelect step in the plan

### Actual results

There are 2 PgSelect steps

### Additional context

Additional discussion in this discord thread:

https://discord.com/channels/489127045289476126/1325736426587033652/1325879877576032288

### Possible Solution

Not sure without digging into PgSelect code