Three static collections are populated once and read-many during hot paths. FrozenSet/FrozenDictionary (net8+) give faster lookups than regular HashSet/Dictionary:

1. TUnit.Core/Discovery/ObjectGraphDiscoverer.cs:52 — SkipTypes (HashSet, 6 entries). Used in ShouldSkipType checks during per-test object-graph traversal.

   private static readonly HashSet<Type> SkipTypes = [typeof(string), typeof(decimal), ...];

2. TUnit.Engine/Discovery/ReflectionTestDataCollector.cs:203 — ExcludedAssemblyNames (HashSet, 20+ entries). Used in Contains(name) per assembly during reflection discovery.

3. TUnit.Core/Helpers/TupleFactory.cs:10 — TypedFactories (Dictionary<Type, Func<object?[], object?>>, 6 entries). Read-only after static ctor finishes; TryGetValue called per tuple-arg conversion.

Fix: declare as FrozenSet<T> / FrozenDictionary<K,V> and initialize via .ToFrozenSet() / .ToFrozenDictionary() at the end of the static initializer.

Why hot: All three are queried inside per-test or per-assembly loops.
TFM: FrozenSet/FrozenDictionary are net8+. TUnit.Core multi-targets netstandard2.0 — guard with #if NET8_0_OR_GREATER and use IReadOnlySet<>/IReadOnlyDictionary<,> field type, or keep HashSet/Dictionary on netstandard2.0 fallback.