Add copy constructor and TryAdd to SmallDictionary - #31

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-dotnet@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Parameter 'value' has no matching param tag in the XML comment for 'SmallDictionaryDebugView<TKey, TValue>.DictionaryEntry.DictionaryEntry(TKey, TValue)' (but other parameters do)