Match call-site paren on multi-line function calls

[mike-at-home]

Summary

This PR updates our Swift formatting rules to enable callsiteparen = balanced, which ensures consistent placement of parentheses and arguments in multiline function calls. With this option, the opening and closing parentheses are always balanced across lines, improving readability and making edits and diffs more predictable. It also works seamlessly with trailing commas to simplify future changes.

---

Reasoning

Currently, multiline function calls can inconsistently close the parenthesis on the same line as the last argument:

let result = executeRequest(
  request,
  onSuccess: { ... },
  onFailure: { ... })

With callsiteparen = balanced, this becomes:

let result = executeRequest(
  request,
  onSuccess: { ... },
  onFailure: { ... }
)

Benefits

• Predictable structure
  The closing parenthesis always appears vertically aligned with the opening parenthesis, reducing visual clutter and ambiguity - particularly with SwiftUI chains.

Before - setBehaviors is aligned with the arguments.

AttributedLabel.groupItem(
  dataID: DataID.subtitleLabel,
  content: .stylableText(subtitle),
  style: style.subtitleFont)
  .setBehaviors { [weak self] context in
    guard let self else { return }
    context.constrainable.numberOfLines = style.subtitleNumberOfLines
  }

After - setBehaviors is aligned with what it is modifying.

AttributedLabel.groupItem(
  dataID: DataID.subtitleLabel,
  content: .stylableText(subtitle),
  style: style.subtitleFont
)
.setBehaviors { [weak self] context in
  guard let self else { return }
  context.constrainable.numberOfLines = style.subtitleNumberOfLines
}

• Simplifies use of trailing commas
  Trailing commas make adding or removing parameters much cleaner and reduce diff noise:

let result = executeRequest(
  request,
  onSuccess: { ... },
  onFailure: { ... },
)

Adding another argument:

  onFailure: { ... },
+ completion: { ... },
)

Removing an argument:

- onFailure: { ... },
)

• Easier visual diffing
  The uniform style prevents mismatched or ambiguous closings, which is especially useful in large nested calls.

• Community alignment
  This approach is common in modern Swift style guides and is fully supported by swift-format and swiftlint.

---

Conclusion

Enabling callsiteparen = balanced gives us consistent, clear multiline call formatting that reduces code review noise and makes refactoring safer.

[calda]

@mike-at-home, can you make the corresponding changes to the readme? This PR only changes the config file.

[calda]

Feel free to make all of the changes in #306 since we are landing both of these changes together