Remove warning for unhandled NWError cases

[dpad85]

This PR removes a compile-time warning in the ios-crypto project, in NativeSocket.swift.

Warning example:

> Task :lightning-kmp-ios-crypto:buildCryptoMacosx
... ios-crypto/PhoenixCrypto/Classes/NativeSocket.swift:105:5: warning: switch must be exhaustive
        switch error {
        ^
...ios-crypto/PhoenixCrypto/Classes/NativeSocket.swift:105:5: note: add missing case: '.wifiAware(_)'
        switch error {
        ^

Should unhandled cases trigger a warning?

The @unknown annotation has been explicitly added in the switch to warn that an error type is unhandled, and that we should do something about it.

In this case, this type is wifiAware, added by Apple in 2025.

However, I think it does not deserve a warning. The switch actually just helps printing a slightly more precise error log, in debug.

Beside, handling a new case such as wifiAware case would either mean:

• forcing the project to use Xcode 26+
• adding many lines of code to handle wifiAware on Xcode26+, while keeping the compile-time warning on older Xcode versions.

It's not worth it. So instead I removed @unknown and just keep default:. This way, unhandled cases will use the default log.