reduce delegate instantiations

[JamesYFC]

Across the projects I've been using this library in, delegate instantiation costs haven't been an issue.

Still, this is a possible improvement.

e.g.

https://devblogs.microsoft.com/dotnet/understanding-the-cost-of-csharp-delegates/#workarounds https://devblogs.microsoft.com/dotnet/understanding-the-cost-of-csharp-delegates/#comment-10168