zc he 5832823dff
fix: flatten of empty closures (#15374)
Closes #15373

# Description

Now `ast -f "{||}"` will return

```
╭─content─┬─────shape─────┬─────span──────╮
│ {||}    │ shape_closure │ ╭───────┬───╮ │
│         │               │ │ start │ 0 │ │
│         │               │ │ end   │ 4 │ │
│         │               │ ╰───────┴───╯ │
╰─────────┴───────────────┴───────────────╯
```

Similar to those of `ast -f "[]"`/`ast -f "{}"`

# User-Facing Changes

# Tests + Formatting

I didn't find the right place to do the test, except for the examples of
`ast` command.

# After Submitting
2025-03-21 06:35:18 -05:00
..