[norman93sun]

Description

Adds the iOS device identifier of the iPhone Duo. Without it IosDeviceInfo.modelName returns Unknown device on that phone.

Identifier	Name
iPhone19,4	iPhone Duo

#3993 added iPhone 18 Pro (iPhone19,2) and iPhone 18 Pro Max (iPhone19,3, iPhone19,7) and left iPhone19,4 out, because the macOS 27.0 device table listed it with no marketing name yet. Xcode 27.1 names that identifier iPhone Duo.

The identifier and name come from:

• Xcode 27.1 simulator device type: modelIdentifier iPhone19,4, product class V68, name iPhone Duo.
• AppleDB and iOS Ref, which both list iPhone19,4 as iPhone Duo.
• The device-code list discussion, where the Xcode 27.1 beta reading is iPhone19,4 : iPhone Duo.

iPhone19,1, iPhone19,5, and iPhone19,6 are left out. They still have no confirmed marketing name, and this change keeps them as Unknown device.

How it was checked: DeviceIdentifiers.m compiles with -Wall -Werror for the iOS device SDK and the simulator SDK. A small harness calling +userKnownDeviceModel: returns iPhone Duo for iPhone19,4, still returns Unknown device for iPhone19,1, and returns the same names as before for iPhone19,2, iPhone19,3, iPhone19,7, and iPhone18,4. No Dart sources, CHANGELOG.md, or plugin version were changed.

Related Issues

None.

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the plugin version in pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.