CombineExt 1.9.0

This version includes some code cleanups and fixes. I've also decided to stop supporting CocoaPods and Carthage due to its low demand volume and the maintenance burden it creates, and focusing on SPM solely for now.

• Fix generic name shadowing in #166
• Fixes WithLatestFrom concurrency issues #163 and #171
• Fix memory leaks in PassthroughRelay in #168 (Thanks @just1103 !)
• Fix buld issues and bump CI to support Xcode 26.0 & Xcode 16.4 only