Feature request: @_spi support

[aim2120]

Hi! I wanted to raise a feature request for @_spi support in mocked types.

For example:

// Module1
protocol MyService {
  @_spi(MyServiceInternal) func secret()
}

What would be needed to support the above:

• The ability to add @_spi(...) import statements to the generated mocks alongside other imports.
• The ability to add @_spi(...) to generate mock properties and functions that had @_spi annotations in the original type.

As a workaround today, I have to manually edit generated mocks to add both of the above features and commit those hand-edited files. It would be amazing for Cuckoo to support this (if I have time, I may take a stab at adding this feature).

[MatyasKriz]

Cuckoo already supports @available annotations, so this might be a simple matter of extending the Attribute enum and extending Crawler implementation.