feat: add option to ignore unexported interface methods instead of error returning

[necrosisoff]

• added -u option to gen command
• don't return an error if option set
• remove unexperted method from list if option set

[jaggman]

@hexdigest will you add this?
It'll useful for generate gRPC wrappers

[hexdigest]

I don’t think ignoring unexported methods is the right solution. If an interface embeds an unexported method, that is usually intentional: the package author is preventing external implementations (including mocks). Skipping that method produces a type that does not actually implement the source interface, which can be misleading.

For gRPC or other generated APIs, the better pattern is usually to define a local consumer-side interface with only the methods the package actually needs, then generate mocks/wrappers against that local interface instead of the full generated interface. This also avoids coupling tests to the entire generated API surface.

If your code depends on the server/client interface defined in some other package (e.g. generated gRPC code) you're doing something wrong and it's a bad Go code. I don't think that promoting this anti-pattern via -u is a good idea.