Support Vec `.push` and `.extend` with the new `TryClone` trait

[amunra]

It would be nice if Rust had an explicit way to distinguish alloc-free cloning vs alloc-dependent cloning, but his isn't there, as such existing implementations for element push / extend still rely on the Clone trait and we're simply hoping for the best.

I don't think that will change, but since we've introduced a new TryClone trait that allows failing gracefully on allocation errors, we should support this in our API too.

A basic use case is simply having vectors of vectors. The following should work:

let mut v: Vec<Vec<i32, MyAlloc>, MyAlloc> = Vec::new_in(alloc);
v.extend(...)?;