[networks]: add decoder/encoder to Attachment and NetworkStatus (#1216)

## Type of Change
- [x] Bug fix
- [ ] New feature  
- [x] Breaking change
- [ ] Documentation update

## Motivation and Context

Adds backward-compatible JSON decoding/encoding fallback for
`Attachment` and `NetworkStatus` to prevent `keyNotFound` errors when
communicating with older `container-apiserver` versions.

Temporary fix but closes #1196

## Testing

Tests ✅ based on comment
[here](https://github.com/apple/container/issues/1196#issuecomment-3902754548)

---------

Co-authored-by: Ed Saipetch <ed@twentybelow.com>

Sources/ContainerResource/Network/Attachment.swift

@@ -51,4 +51,52 @@ public struct Attachment: Codable, Sendable {
         self.macAddress = macAddress
         self.mtu = mtu
     }
+
+    enum CodingKeys: String, CodingKey {
+        case network
+        case hostname
+        case ipv4Address
+        case ipv4Gateway
+        case ipv6Address
+        case macAddress
+        case mtu
+        // TODO: retain for deserialization compatibility for now, remove later
+        case address
+        case gateway
+    }
+
+    /// Create a configuration from the supplied Decoder, initializing missing
+    /// values where possible to reasonable defaults.
+    public init(from decoder: Decoder) throws {
+        let container = try decoder.container(keyedBy: CodingKeys.self)
+
+        network = try container.decode(String.self, forKey: .network)
+        hostname = try container.decode(String.self, forKey: .hostname)
+        if let address = try? container.decode(CIDRv4.self, forKey: .ipv4Address) {
+            ipv4Address = address
+        } else {
+            ipv4Address = try container.decode(CIDRv4.self, forKey: .address)
+        }
+        if let gateway = try? container.decode(IPv4Address.self, forKey: .ipv4Gateway) {
+            ipv4Gateway = gateway
+        } else {
+            ipv4Gateway = try container.decode(IPv4Address.self, forKey: .gateway)
+        }
+        ipv6Address = try container.decodeIfPresent(CIDRv6.self, forKey: .ipv6Address)
+        macAddress = try container.decodeIfPresent(MACAddress.self, forKey: .macAddress)
+        mtu = try container.decodeIfPresent(UInt32.self, forKey: .mtu)
+    }
+
+    /// Encode the configuration to the supplied Encoder.
+    public func encode(to encoder: Encoder) throws {
+        var container = encoder.container(keyedBy: CodingKeys.self)
+
+        try container.encode(network, forKey: .network)
+        try container.encode(hostname, forKey: .hostname)
+        try container.encode(ipv4Address, forKey: .ipv4Address)
+        try container.encode(ipv4Gateway, forKey: .ipv4Gateway)
+        try container.encodeIfPresent(ipv6Address, forKey: .ipv6Address)
+        try container.encodeIfPresent(macAddress, forKey: .macAddress)
+        try container.encodeIfPresent(mtu, forKey: .mtu)
+    }
 }

Sources/ContainerResource/Network/NetworkConfiguration.swift

@@ -80,7 +80,7 @@ public struct NetworkConfiguration: Codable, Sendable, Identifiable {
         case ipv6Subnet
         case labels
         case pluginInfo
-        // TODO: retain for deserialization compatability for now, remove later
+        // TODO: retain for deserialization compatibility for now, remove later
         case subnet
     }
 

Sources/ContainerResource/Network/NetworkState.swift

@@ -39,6 +39,43 @@ public struct NetworkStatus: Codable, Sendable {
         self.ipv4Gateway = ipv4Gateway
         self.ipv6Subnet = ipv6Subnet
     }
+
+    enum CodingKeys: String, CodingKey {
+        case ipv4Subnet
+        case ipv4Gateway
+        case ipv6Subnet
+        // TODO: retain for deserialization compatibility for now, remove later
+        case address
+        case gateway
+    }
+
+    /// Create a configuration from the supplied Decoder, initializing missing
+    /// values where possible to reasonable defaults.
+    public init(from decoder: Decoder) throws {
+        let container = try decoder.container(keyedBy: CodingKeys.self)
+
+        if let address = try? container.decode(CIDRv4.self, forKey: .ipv4Subnet) {
+            ipv4Subnet = address
+        } else {
+            ipv4Subnet = try container.decode(CIDRv4.self, forKey: .address)
+        }
+        if let gateway = try? container.decode(IPv4Address.self, forKey: .ipv4Gateway) {
+            ipv4Gateway = gateway
+        } else {
+            ipv4Gateway = try container.decode(IPv4Address.self, forKey: .gateway)
+        }
+        ipv6Subnet = try container.decodeIfPresent(String.self, forKey: .ipv6Subnet)
+            .map { try CIDRv6($0) }
+    }
+
+    /// Encode the configuration to the supplied Encoder.
+    public func encode(to encoder: Encoder) throws {
+        var container = encoder.container(keyedBy: CodingKeys.self)
+
+        try container.encode(ipv4Subnet, forKey: .ipv4Subnet)
+        try container.encode(ipv4Gateway, forKey: .ipv4Gateway)
+        try container.encodeIfPresent(ipv6Subnet, forKey: .ipv6Subnet)
+    }
 }
 
 /// The configuration and runtime attributes for a network.