Sync code from fork back to upstream

[Kyle-Ye]

• Bump Swift version to 5.7
• Remove Cocoapods support
• Add library evolution support
• Add OSUnfairRecursiveLock support
• Add Zip, Merge, CombineLatest implementation
• Fix watchOS and tvOS build issue
• Fix compiler warning about Swift 6's generic rule

Maybe we can consider renaming the default branch from "master" to "main" too :)

[!NOTE] The branch upstream will be fork/main plus a commit for reverting back the README change and default branch name.

Future plan

• [ ] Release a new version
• [ ] Fix ObservedObject bug
• [ ] Migrating from XCTest to swift-testing