Fix Linux CI: wrap snapshot tests in #if canImport(Darwin)

The #TestSuites macro only generates Test.Snapshot suite on Darwin
platforms. Wrapped all Test.Snapshot extensions with conditional
compilation to fix Linux build failures.

Author: coenttb

Tests/HTML Tests/CSS Tests.swift

@@ -16,6 +16,7 @@ enum CSSNamespace {
 
 // MARK: - Snapshot Tests - Fluent Chaining
 
+#if canImport(Darwin)
 extension CSSNamespace.Test.Snapshot {
     @Test("Fluent chaining without repeated .css calls")
     func fluentChaining() {
@@ -1119,6 +1120,7 @@ extension CSSNamespace.Test.Snapshot {
         }
     }
 }
+#endif
 
 // MARK: - Unit Tests - CSS Color
 
@@ -1200,6 +1202,7 @@ extension CSSNamespace.Test.Unit {
 
 // MARK: - Snapshot Tests - Color with HTML
 
+#if canImport(Darwin)
 extension CSSNamespace.Test.Snapshot {
     @Test("General color styling")
     func general1() {
@@ -1438,6 +1441,7 @@ extension CSSNamespace.Test.Snapshot {
         }
     }
 }
+#endif
 
 // MARK: - Test Helpers
 

Tests/HTML Tests/DarkModeColor Tests.swift

@@ -126,6 +126,7 @@ extension DarkModeColor.Test.Unit {
 
 // MARK: - Snapshot Tests
 
+#if canImport(Darwin)
 extension DarkModeColor.Test.Snapshot {
     @Test("HTMLColor with light only auto-darkens")
     func htmlColorAutoDarken() {
@@ -1052,3 +1053,4 @@ extension DarkModeColor.Test.Snapshot {
         }
     }
 }
+#endif

Tests/HTML Tests/HStack Tests.swift

@@ -16,6 +16,7 @@ enum HStackTests {
 
 // MARK: - Snapshot Tests
 
+#if canImport(Darwin)
 extension HStackTests.Test.Snapshot {
     @Test("HStack renders with default settings")
     func hstack() {
@@ -59,3 +60,4 @@ extension HStackTests.Test.Snapshot {
         }
     }
 }
+#endif

Tests/HTML Tests/HTML.Document Tests.swift

@@ -129,6 +129,7 @@ private struct _CustomButton: HTML.View {
 
 // MARK: - Snapshot Tests
 
+#if canImport(Darwin)
 extension HTMLDocumentTests.Test.Snapshot {
     @Test("Full document example")
     func fullDocumentExample() {
@@ -219,3 +220,4 @@ extension HTMLDocumentTests.Test.Snapshot {
         }
     }
 }
+#endif

Tests/HTML Tests/LazyVGrid Tests.swift

@@ -18,6 +18,7 @@ enum LazyVGridTests {
 
 // MARK: - Snapshot Tests
 
+#if canImport(Darwin)
 extension LazyVGridTests.Test.Snapshot {
     @Test("LazyVGrid with fractions columns")
     func lazyVGrid() {
@@ -116,3 +117,4 @@ extension LazyVGridTests.Test.Snapshot {
         }
     }
 }
+#endif

Tests/HTML Tests/Spacer Tests.swift

@@ -16,6 +16,7 @@ extension Spacer {
 
 // MARK: - Snapshot Tests
 
+#if canImport(Darwin)
 extension Spacer.Test.Snapshot {
     @Test("Spacer pushes items apart in HStack")
     func spacer() {
@@ -41,3 +42,4 @@ extension Spacer.Test.Snapshot {
         }
     }
 }
+#endif

Tests/HTML Tests/TranslatedString+HTML Tests.swift

@@ -21,6 +21,7 @@
 
     // MARK: - Snapshot Tests
 
+    #if canImport(Darwin)
     extension TranslatedStringHTML.Test.Snapshot {
         @Test("TranslatedString renders as HTML")
         func translatedStringRendersAsHTML() {
@@ -241,4 +242,5 @@
             }
         }
     }
+    #endif
 #endif

Tests/HTML Tests/VStack Tests.swift

@@ -16,6 +16,7 @@ enum VStackTests {
 
 // MARK: - Snapshot Tests
 
+#if canImport(Darwin)
 extension VStackTests.Test.Snapshot {
     @Test("VStack renders with default settings")
     func vstack() {
@@ -59,3 +60,4 @@ extension VStackTests.Test.Snapshot {
         }
     }
 }
+#endif