[docs] Make C++ example for advantagescope swerve states compilable

[nobody5050]

When I was initially implementing this in my codebase the example in the docs confused me because although it seemed straightforward it wouldn’t actually compile. The publisher needs a std::span of states rather than a vector as indicated by the docs. While this is definitely not the most concise implementation, (it’s ripped from our season code) it’s a lot more helpful in my opinion.

[PeterJohnson]

It shouldn't be necessary to explicitly create a std::span. It should work to just pass states_vec directly to the publisher, as there's an implicit conversion from std::vector to std::span.

[PeterJohnson]

It should also be possible to simply use double-braces here, although I've not tested it:

swervePublisher.Set(
            {{
              frontLeftState,
              frontRightState,
              backLeftState,
              backRightState
            }}
          );