feat(ios): Add Swift Package Manager (SPM) support

[TheoGermain]

Closes #176.

Summary

Adds a Package.swift manifest for the iOS plugin so apps using Flutter's
Swift Package Manager integration can resolve mixpanel_flutter natively
instead of falling back to CocoaPods. CocoaPods consumers are unaffected —
the .podspec still works and is unchanged in semantics.

The scope of this PR is iOS only. macOS still uses CocoaPods; SPM support
for macOS can be added in a follow-up since it is largely the same pattern.

What changed

Area	Change
ios/mixpanel_flutter/Package.swift	New SPM manifest. Single pure-Swift target. Depends on mixpanel-swift 6.3.0 (pinned to the same exact version as the podspec). iOS 12.0 minimum (matches the podspec).
ios/mixpanel_flutter/Sources/mixpanel_flutter/	Swift sources moved to the SPM-expected layout. The two files are symlinks back to the canonical shared sources in swift/Classes/, mirroring the pattern already used by macos/Classes/.
ios/mixpanel_flutter.podspec	source_files updated to point at the new Sources/ directory.
swift/Classes/SwiftMixpanelFlutterPlugin.swift	Added @objc(MixpanelFlutterPlugin) to expose the Swift class to Obj-C registrants under the same name as the previous Obj-C wrapper. This preserves backwards compatibility for projects with an Obj-C AppDelegate.
ios/Classes/	Removed. The Obj-C wrapper (.h/.m) is no longer needed since the Swift class is now @objc-exposed under the expected name. The old Swift symlinks here are replaced by the equivalent ones under the new Sources/ layout.

Why eliminate the Obj-C wrapper

The previous MixpanelFlutterPlugin.{h,m} only existed to bridge from
Obj-C-named MixpanelFlutterPlugin → Swift SwiftMixpanelFlutterPlugin.
Mixed Swift+Obj-C SPM targets are awkward (SPM does not natively support
mixed-language targets in a single module).

By annotating the Swift class with @objc(MixpanelFlutterPlugin):

• Obj-C consumers (legacy AppDelegate.m projects) still find the class as
  MixpanelFlutterPlugin — no behavior change.
• Swift consumers continue to use either name.
• The SPM manifest can stay simple (single Swift target).

This mirrors the approach already taken on macOS (where a Swift typealias
serves the same purpose, no Obj-C wrapper).

Verification

• flutter pub get succeeds in example/ with SPM enabled
  (flutter config --enable-swift-package-manager)
• flutter run builds and launches on an iOS simulator with SPM enabled
• flutter run builds and launches on an iOS simulator with SPM disabled
  (CocoaPods path)
• pod lib lint ios/mixpanel_flutter.podspec still passes
• Obj-C AppDelegate consumers still resolve MixpanelFlutterPlugin
  via the auto-generated registrant

Follow-ups (out of scope here)

• Add SPM support for macOS (mirrors this change in macos/).
• Bump the iOS minimum to 13.0 once Update SDK for Flutter 3.35 compatibility #208 lands (currently keeping 12.0 to
  match the existing podspec).

References

• Flutter docs — Swift Package Manager for plugin authors
• mixpanel-swift already supports SPM (Mixpanel/Package.swift)

[ketanmixpanel]

Thanks for the detailed PR @TheoGermain, really appreciate the writeup and the verification checklist. I'll review and update here.

[ketanmixpanel]

Hi @TheoGermain, I tried running the example app with SPM enabled and the build is failing with the error below. Can you confirm if it works on your end?

An error occurred when adding Swift Package Manager integration:
  Error: Unable to get Xcode project information:
 2026-05-12 14:41:08.488 xcodebuild[48151:426773] Writing error result bundle to
 /var/folders/zt/q91rmj8551b03mjskx4k5_cw0000gn/T/ResultBundle_2026-12-05_14-41-0008.xcresult
xcodebuild: error: Could not resolve package dependencies:
  unable to override package 'mixpanel_flutter' because its identity 'mixpanel-flutter' doesn't match override's identity (directory name) 'mixpanel_flutter'
  fatalError

Thanks!

[TheoGermain]

Hi @ketanmixpanel, good catch — thank you for testing!

The root cause is an SPM package identity mismatch. SPM derives a package's identity from the directory name for local path overrides. Flutter was pointing at the ios/mixpanel_flutter/ directory (underscore), but the canonical identity from the repository URL github.com/mixpanel/mixpanel-flutter is mixpanel-flutter (hyphen). These two identities don't match, hence the error.

I just pushed a fix (aae8970) that makes three changes:

1. Renames ios/mixpanel_flutter/ → ios/mixpanel-flutter/ so the directory-based identity matches the URL identity.
2. Updates Package.swift name: "mixpanel_flutter" → name: "mixpanel-flutter" to be consistent.
3. Adds swiftPackageName: mixpanel-flutter to pubspec.yaml under the ios: platform so Flutter's toolchain knows to look in ios/mixpanel-flutter/ rather than the default ios/mixpanel_flutter/.

The podspec source_files path is also updated accordingly. Could you try re-running the example with the updated branch? Thanks!