fix(rust): Rust example

[carlocorradini]

Unfortunately, the Rust example does not compile due to waitset.attach(&status_condition)? call.
waitset.attach requires the entity E to implement HasStatusCondition. However, HasStatusCondition<T> is only implemented for DataReader<T>. Therefore, the correct call should be waitset.attach(&reader)?;.

Before:

let status_condition = reader.get_status_condition();
let mut waitset = hdds::WaitSet::new();
waitset.attach(&status_condition)?;

After:

let mut waitset = hdds::WaitSet::new();
waitset.attach(&reader)?;

[hdds-team]

Great catch, and your diagnosis is exactly right: WaitSet::attach takes an entity that implements HasStatusCondition (i.e. the DataReader), not the condition object - so attach(&reader)? is correct.

Full disclosure: that snippet in docs/examples/multi-topic.md predates our doc-compile checks and has drifted from the API in a couple more spots (WaitSet::new() returns Self not a Result, wait() takes Option, and read_condition() should be get_status_condition()). So the real fix touches a few lines. The 07_advanced/waitsets.rs sample is a known-good reference for the correct idiom.

If you'd like to open the PR against that doc, I'd be happy to review it - otherwise I'll get it corrected. Either way, thanks for the sharp report! 🙏