Sign the BenchmarkDotNet NuGet package

This is a request for the BenchmarkDotNet NuGet package to have [signed](https://learn.microsoft.com/en-us/nuget/create-packages/sign-a-package) DLLs included. This would reduce friction when trying to use this package in security-sensitive projects/organizations.

My understanding is that such signatures require a certificate purchase, so I would understand if it is not practical at this time to do code signing, but I wanted put the request out there.