support traits in impls

[incertia]

test_fuzz_impl fails to correctly extract T: Trait from impl <T: Trait> Struct<T> and apply it to Args when fuzzing the impl functions. See daf5440 for some basic work trying to address this.

[smoelius]

This is starting to come back to me now.

Not putting the traits in Args was intentional because doing so can cause serde_derive to fail in some cases. (Related: rust-lang/rust-clippy#1689, rust-lang/api-guidelines#6)

But as recent experience shows, it's needed in some cases.

So I'm wondering what the best way to handle this is. A macro option to include the traits in Args?

[smoelius]

For syntax, I'm leaning toward something like:

#[test_fuzz(bound("T"))]