fix: serialize snapshot tests with @mainactor parent suite

Implement SnapshotTests parent suite pattern from swift-structured-queries-postgres
to fix SIGSEGV crashes on Linux CI runners. The @mainactor attribute on the parent
suite ensures all child test suites run serially, avoiding parallel execution issues
with swift-snapshot-testing on Linux.

Changes:
- Add Support/SnapshotTests.swift with @mainactor parent suite
- Convert all 93 HTMLElementsPointFreeHTML test files to extend SnapshotTests
- Each test suite now runs as a child of the serialized parent suite

Pattern applied:
```swift
extension SnapshotTests {
    @suite struct ElementTests {
        // tests...
    }
}
```

This resolves the signal 11 (SIGSEGV) crashes observed in CI runs on both
Ubuntu Swift 6.2 and 6.0 compatibility jobs.

Author: coenttb

Tests/HTMLCSSPointFreeHTML Tests/HTMLCSSPointFree Tests.swift

@@ -14,7 +14,7 @@ import Testing
 
 @Suite(
     "HTML+CSS+PointFreeHTML Tests",
-    .snapshots(record: .missing)
+    .snapshots(record: .failed)
 )
 struct IntegrationTests {
     @Test("HTML element with attributes and styles")
@@ -69,7 +69,7 @@ struct IntegrationTests {
 
     @Test(
         "General3",
-        .snapshots(record: .missing)
+        .snapshots(record: .failed)
     )
     func general3() {
         assertInlineSnapshot(

Tests/HTMLElementsPointFreeHTML Tests/Support/SnapshotTests.swift

@@ -0,0 +1,9 @@
+import SnapshotTesting
+import Testing
+
+@MainActor
+@Suite(
+  //    .serialized,
+  .snapshots(record: .missing)
+)
+struct SnapshotTests {}

Tests/HTMLElementsPointFreeHTML Tests/a Anchor Tests.swift

@@ -4,11 +4,12 @@ import InlineSnapshotTesting
 import PointFreeHTMLTestSupport
 import Testing
 
-@Suite(
-    "Anchor Element Tests",
-    .snapshots(record: .missing)
-)
-struct AnchorTests {
+extension SnapshotTests {
+    @Suite(
+        "Anchor Element Tests",
+        .snapshots(record: .failed)
+    )
+    struct AnchorTests {
     @Test("Basic anchor renders correctly")
     func basicAnchorRendersCorrectly() {
         assertInlineSnapshot(
@@ -109,4 +110,5 @@ struct AnchorTests {
       """
         }
     }
+    }
 }

Tests/HTMLElementsPointFreeHTML Tests/abbr Abbreviation Tests.swift

@@ -6,7 +6,7 @@
 //
 // @Suite(
 //    "Abbreviation Element Tests",
-//    .snapshots(record: .missing),
+//    .snapshots(record: .failed),
 // )
 // struct AbbreviationTests {
 //    @Test("Basic abbreviation renders correctly")

Tests/HTMLElementsPointFreeHTML Tests/address Contact Address Tests.swift

@@ -4,11 +4,12 @@ import InlineSnapshotTesting
 import PointFreeHTMLTestSupport
 import Testing
 
-@Suite(
-    "Address Element Tests",
-    .snapshots(record: .missing)
-)
-struct AddressTests {
+extension SnapshotTests {
+    @Suite(
+        "Address Element Tests",
+        .snapshots(record: .failed)
+    )
+    struct AddressTests {
     @Test("Basic address renders correctly")
     func basicAddressRendersCorrectly() {
         assertInlineSnapshot(
@@ -276,4 +277,5 @@ struct AddressTests {
       """
         }
     }
+    }
 }

Tests/HTMLElementsPointFreeHTML Tests/area Image Map Area Tests.swift

@@ -4,11 +4,12 @@ import InlineSnapshotTesting
 import PointFreeHTMLTestSupport
 import Testing
 
-@Suite(
-    "Area Element Tests",
-    .snapshots(record: .missing)
-)
-struct AreaTests {
+extension SnapshotTests {
+    @Suite(
+        "Area Element Tests",
+        .snapshots(record: .failed)
+    )
+    struct AreaTests {
     @Test("Basic area renders correctly")
     func basicAreaRendersCorrectly() {
         assertInlineSnapshot(
@@ -76,4 +77,5 @@ struct AreaTests {
       """
         }
     }
+    }
 }

Tests/HTMLElementsPointFreeHTML Tests/article Article Contents Tests.swift

@@ -4,11 +4,12 @@ import InlineSnapshotTesting
 import PointFreeHTMLTestSupport
 import Testing
 
-@Suite(
-    "Article Element Tests",
-    .snapshots(record: .missing)
-)
-struct ArticleTests {
+extension SnapshotTests {
+    @Suite(
+        "Article Element Tests",
+        .snapshots(record: .failed)
+    )
+    struct ArticleTests {
     @Test("Basic article renders correctly")
     func basicArticleRendersCorrectly() {
         assertInlineSnapshot(
@@ -223,4 +224,5 @@ struct ArticleTests {
       """
         }
     }
+    }
 }

Tests/HTMLElementsPointFreeHTML Tests/aside Aside Tests.swift

@@ -4,11 +4,12 @@ import InlineSnapshotTesting
 import PointFreeHTMLTestSupport
 import Testing
 
-@Suite(
-    "Aside Element Tests",
-    .snapshots(record: .missing)
-)
-struct AsideTests {
+extension SnapshotTests {
+    @Suite(
+        "Aside Element Tests",
+        .snapshots(record: .failed)
+    )
+    struct AsideTests {
     @Test("Basic aside renders correctly")
     func basicAsideRendersCorrectly() {
         assertInlineSnapshot(
@@ -313,4 +314,5 @@ struct AsideTests {
       """
         }
     }
+    }
 }

Tests/HTMLElementsPointFreeHTML Tests/audio Embed Audio Tests.swift

@@ -4,11 +4,12 @@ import InlineSnapshotTesting
 import PointFreeHTMLTestSupport
 import Testing
 
-@Suite(
-    "Embed Audio Element Tests",
-    .snapshots(record: .missing)
-)
-struct AudioTests {
+extension SnapshotTests {
+    @Suite(
+        "Embed Audio Element Tests",
+        .snapshots(record: .failed)
+    )
+    struct AudioTests {
     @Test("Basic audio renders correctly")
     func basicAudioRendersCorrectly() {
         assertInlineSnapshot(
@@ -184,4 +185,5 @@ struct AudioTests {
       """
         }
     }
+    }
 }

Tests/HTMLElementsPointFreeHTML Tests/b Bring Attention To Tests.swift

@@ -4,11 +4,12 @@ import InlineSnapshotTesting
 import PointFreeHTMLTestSupport
 import Testing
 
-@Suite(
-    "B Element Tests",
-    .snapshots(record: .missing)
-)
-struct BTests {
+extension SnapshotTests {
+    @Suite(
+        "B Element Tests",
+        .snapshots(record: .failed)
+    )
+    struct BTests {
     @Test("Basic b element renders correctly")
     func basicBElementRendersCorrectly() {
         assertInlineSnapshot(
@@ -90,4 +91,5 @@ struct BTests {
       """
         }
     }
+    }
 }