fix: Preserve nested tuple parentheses

[lprnmns]

For reviewers

• I did not use AI
• I used AI and thoroughly reviewed every code/docs change

Description of the change

Keep tuple-context flags local to the immediate AST node. Previously, a subscript or comprehension-target flag could flow through a nested list, call, or comprehension and remove tuple parentheses below it. This changed the rendered AST in cases such as o[f((x, y))] and could produce invalid Python for a tuple-valued comprehension nested in a subscript.

Four round-trip regressions cover nested containers, calls, comprehensions, and destructuring targets.

Validation:

• Focused regression: 4 passed
• PYTHON_VERSIONS='' ./scripts/make format check test — passed
• Additional deterministic expression matrix — 861 valid cases, 0 failures

Relevant resources

• Independent reproduction on current main; no issue was required to reproduce it.
• Existing PR fix: keep parentheses around top-level named expressions (walrus) #480 concerns only top-level named expressions and does not overlap this change.

[pawamoy]

Thanks! Found a simplification 🙂 Let me know what you think.

[lprnmns]

The simplification looks good to me and keeps the context behavior covered. Thanks for the fixup.