NSubstitute 7.0.0 roadmap proposal

[Romfos]

I propose to implement changes in following areas for the next major release:

Infrastructure:

• Future .NET 11 support (could be done in 6.x.x as update)

Update dependencies:

• Migrate to Castle.Core 6.0.0]

Code cleanup:

• Remove obsolete CompatArg and Arg.Compat

Features:

• Support by-ref parameters #992

Please join to the discussion

cc @dtchepak @alexandrnikitin @tpodolak @304NotModified