fix(Platform): make arm64 nil-variant and v8 hash identically

Sources/ContainerizationOCI/Platform.swift

@@ -277,7 +277,14 @@ extension Platform: Hashable {
     }
 
     public func hash(into hasher: inout Swift.Hasher) {
-        hasher.combine(description)
+        hasher.combine(os)
+        hasher.combine(architecture)
+        // arm64 with no variant is equivalent to arm64/v8 per the == implementation
+        if architecture == "arm64" {
+            hasher.combine(variant ?? "v8")
+        } else {
+            hasher.combine(variant)
+        }
     }
 }
 

Tests/ContainerizationOCITests/OCIPlatformTests.swift

@@ -66,4 +66,19 @@ struct OCIPlatformTests {
         let rhs = Platform(arch: "arm64", os: "linux", variant: nil)
         #expect(lhs == rhs, "Both nil variants => variantEqual is true => overall equal")
     }
+
+    @Test func arm64_nilAndV8_sameHashValue() {
+        let withoutVariant = Platform(arch: "arm64", os: "linux", variant: nil)
+        let withV8 = Platform(arch: "arm64", os: "linux", variant: "v8")
+        // Equal platforms must produce the same hash — violating this breaks Set/Dictionary lookups
+        #expect(withoutVariant.hashValue == withV8.hashValue, "arm64 nil variant and v8 must hash identically")
+    }
+
+    @Test func arm64_nilAndV8_setLookup() {
+        let withoutVariant = Platform(arch: "arm64", os: "linux", variant: nil)
+        let withV8 = Platform(arch: "arm64", os: "linux", variant: "v8")
+        var set = Set<Platform>()
+        set.insert(withoutVariant)
+        #expect(set.contains(withV8), "arm64/v8 must be found in a Set that contains arm64 with nil variant")
+    }
 }