Support visionOS platform for nostr-swift & nostr-sdk-swift

[ismyhc]

Describe the enhancement
Add support in swift bindings for VisionOS platform

Use case
Id like to use this to build an nostr application for VisionOS

Additional context
I don't know a lot about NDK, but a couple of things I think need to be done.

On the swift side, the Package.swift needs to update to swift-tools-version: 5.9 and .visionOS(.v1) added to platforms. Also, I assume that nostr_sdkFFI xcframework needs to be built for visionOS.

[yukibtc]

Unfortunately rust not support visionOS targets yet: rust-lang/rust#112930

[ismyhc]

Unfortunately rust not support visionOS targets yet: rust-lang/rust#112930

Ah, good to know. Hopefully it can happen in the near term.