dev: Migrate Easydict to Swift 6

[Jerry23011]

Since Apple released Swift 6 on WWDC24, we can try migrating Easydict to the new language mode after Xcode 16's release. This can may help prevent issues that are hard to debug or reproduce like #622

Looking at the number of warnings after turning on strict concurrency checking under Xcode 15, there will be quite a lot of things to do. We would also need to wait for some packages to migrate.

https://www.swift.org/migration/documentation/migrationguide/

[tisfeng]

ok, this might be a big project. Let's push it after Xcode 16 is officially released.