Fix #1234 and ensure documents are disposed in Merge() - #1382

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

Nullability of reference types in type of parameter 'obj' of 'bool OperatorToken.Equals(IToken obj)' doesn't match implicitly implemented member 'bool IEquatable<IToken>.Equals(IToken? other)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'obj' of 'bool BooleanToken.Equals(IToken obj)' doesn't match implicitly implemented member 'bool IEquatable<IToken>.Equals(IToken? other)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'obj' of 'bool ObjectToken.Equals(IToken obj)' doesn't match implicitly implemented member 'bool IEquatable<IToken>.Equals(IToken? other)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'obj' of 'bool ArrayToken.Equals(IToken obj)' doesn't match implicitly implemented member 'bool IEquatable<IToken>.Equals(IToken? other)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'obj' of 'bool NumericToken.Equals(IToken obj)' doesn't match implicitly implemented member 'bool IEquatable<IToken>.Equals(IToken? other)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'obj' of 'bool NullToken.Equals(IToken obj)' doesn't match implicitly implemented member 'bool IEquatable<IToken>.Equals(IToken? other)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'obj' of 'bool NameToken.Equals(IToken obj)' doesn't match implicitly implemented member 'bool IEquatable<IToken>.Equals(IToken? other)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'obj' of 'bool InlineImageDataToken.Equals(IToken obj)' doesn't match implicitly implemented member 'bool IEquatable<IToken>.Equals(IToken? other)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'obj' of 'bool IndirectReferenceToken.Equals(IToken obj)' doesn't match implicitly implemented member 'bool IEquatable<IToken>.Equals(IToken? other)' (possibly because of nullability attributes).