/// Determines item dropping behavior when the container is dropped.
///
/// By default, the container will drop its items when it is dropped.
///
/// # Examples
///
/// ```
/// use pinned_pool::{DropPolicy, PinnedPool};
///
/// // The drop policy is set at pool creation time.
/// let pool = PinnedPool::<u32>::builder()
/// .drop_policy(DropPolicy::MustNotDropItems)
/// .build();
/// ```