Use package traits

[kou]

https://github.com/swiftlang/swift-evolution/blob/main/proposals/0450-swiftpm-package-traits.md

It's available since Swift 6.1.

We can remove Arrow/Package.swift and ArrowFlight/Package.swift by using package traits.

When can we move to Swift 6.1 from Swift 5.10?

[morenonicolelli]

During my check I try to migrate in Swift 6.1: it's not hard but in my opinion something could be re-design to improve "Sendability".

In case, the operation needs some work but not too much