Check for supported types in the @SendableProperty macro (#212)

- The `@SendableProperty` macro now checks for supported types to
prevent a misuse with unsupported types like structs, dictionaries, and
arrays
- The new `@SendablePropertyUnchecked` can be used with classes and
enums

Sources/Containerization/LinuxContainer.swift

@@ -54,7 +54,7 @@ public final class LinuxContainer: Container, Sendable {
         var dns: DNS? = nil
     }
 
-    @SendableProperty
+    @SendablePropertyUnchecked
     private var state: State
 
     private let config: Mutex<Configuration>