fix: warning about OSMacros.h in header

[nan-li]

Description

One Line Summary

Fix warning about umbrella header for module 'OneSignalCore' does not include header 'OSMacros.h' by changing its visibility to private.

Details

OSMacros.h was in the public Headers folder of the framework, but it's not imported by the umbrella header OneSignalCore.h and Clang expects all public headers to be included by that umbrella header.

• Related to changes in fix: Remove exposing var and let macros #1622

How this change was tested

• Built the frameworks with our build script and confirmed the headers are removed from OneSignalCore framework: - 5d88f09
  • iOS_SDK/OneSignalSDK/OneSignal_Core/OneSignalCore.xcframework/ios-arm64/OneSignalCore.framework/Headers/OSMacros.h
  • iOS_SDK/OneSignalSDK/OneSignal_Core/OneSignalCore.xcframework/ios-arm64_x86_64-maccatalyst/OneSignalCore.framework/Versions/A/Headers/OSMacros.h
  • iOS_SDK/OneSignalSDK/OneSignal_Core/OneSignalCore.xcframework/ios-arm64_x86_64-simulator/OneSignalCore.framework/Headers/OSMacros.h
• Then added to another example app via SPM and confirmed SDK works as expected

Motivation

Reported warning internally

.../Developer/Xcode/DerivedData/MyApp-aqklcvntjdtdisejvbxcravmndht/Build/Products/Debug-iphoneos/OneSignalCore.framework/Headers/OneSignalCore.h:70:1 umbrella header for module 'OneSignalCore' does not include header 'OSMacros.h'

Scope

build process and annoying warnings

Testing

Unit testing

None needed

Manual testing

• Build and run example app
• Test built frameworks before release

Affected code checklist

• Notifications
  • Display
  • Open
  • Push Processing
  • Confirm Deliveries
• Outcomes
• Sessions
• In-App Messaging
• REST API requests
• Public API changes

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
• Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• I have included test coverage for these changes, or explained why they are not needed
• All automated tests pass, or I explained why that is not possible
• I have personally tested this on my device, or explained why that is not possible

Final pass

• Code is as readable as possible.
• I have reviewed this PR myself, ensuring it meets each checklist item

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This change is 

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.