Fix parenthesized detection for tuples (#6599)
## Summary
This PR fixes our code for detecting whether a tuple has its own
parentheses, which is necessary when attempting to preserve parentheses.
As-is, we were getting some cases wrong, like `(a := 1), (b := 3))` --
the detection code inferred that this _was_ parenthesized, and so
wrapped the entire thing in an unnecessary set of parentheses.
## Test Plan
`cargo test`
Before:
| project | similarity index |
|--------------|------------------|
| cpython | 0.75472 |
| django | 0.99804 |
| transformers | 0.99618 |
| twine | 0.99876 |
| typeshed | 0.74288 |
| warehouse | 0.99601 |
| zulip | 0.99727 |
After:
| project | similarity index |
|--------------|------------------|
| cpython | 0.75473 |
| django | 0.99804 |
| transformers | 0.99618 |
| twine | 0.99876 |
| typeshed | 0.74288 |
| warehouse | 0.99601 |
| zulip | 0.99727 |
