Remove redundant generator parentheses

[Boulea7]

Description

Closes #2943.

Under --preview, this removes redundant extra parentheses around generator expressions, including standalone expressions, tuple/list/dict values, nested calls, and call arguments where Python still requires one visible pair.

Checklist - did you ...

• Implement any code style changes under the --preview style, following the stability policy?
• Add an entry in CHANGES.md if necessary?
• Add / update tests if necessary?
• Add new / update outdated documentation?

Tests

• .venv/bin/python -m pytest -n 4 -q (551 passed, 2 skipped, 8 subtests passed)
• .venv/bin/python -m pytest tests/test_format.py -q (233 passed)
• .venv/bin/pre-commit run --all-files
• .venv/bin/sphinx-build -a -b html -W docs/ docs/_build/
• Direct and extra-parenthesized generator cases before attribute, subscript, and call trailers

[cobaltt7]

Thanks!

Would it be simple to extend this to all structures? Here's some examples I found:

((item.is_valid() for item in items))  # alone at top level
(((item.is_valid() for item in items)),)  # tuple
[((item.is_valid() for item in items)), ""]  # array (it's already handled when it's the only element)
{"foo": ((item.is_valid() for item in items))}  # dictionary value

[github-actions]

diff-shades results comparing this PR (53f837a) to main (74371e2):

--preview style (View full diff):

╭─────────────────────── Summary ────────────────────────╮
│ 1 projects & 2 files changed / 14 changes [+6/-8]      │
│                                                        │
│ ... out of 3 036 322 lines, 14 116 files & 22 projects │
╰────────────────────────────────────────────────────────╯
Differences found.

--stable style: no changes

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What is this? | Workflow run | diff-shades documentation

[Boulea7]

Yes, that fit cleanly. I expanded this to the structures you listed and added regression cases for top-level expressions, tuple/list/dict values, nested calls, keyword/starred call args, and multi-arg calls where one pair is still required.

Latest checks:

• .venv/bin/python -m pytest tests/test_format.py -q
• in-memory AST/idempotence checks for nested, walrus, async, attribute/subscript, starred, keyword, and multi-arg cases