Function with_htt 

pub fn with_htt<R, F>(htt: &SharedHTT, f: F) -> IntegrationResult<R>
where
    F: FnOnce(&HyperbolicTreeTensor) -> IntegrationResult<R>,

Execute a function with access to a shared HTT instance.

No locking needed: all HyperbolicTreeTensor methods take &self with fine-grained interior mutability (DashMap, Mutex, RwLock).