Implement AsColumnFamilyRef for Arc<Mutex<BoundColumnFamily<'a>>>

[Chaoses-Ib]

In multi-threaded mode, BoundColumnFamily<'a> is marked Send. However, AsColumnFamilyRef is only implemented for Arc<BoundColumnFamily<'a>>, which requires BoundColumnFamily<'a>: Send + Sync to be Send. This causes Arc<BoundColumnFamily<'a>> cannot be sent between threads. Is it possible to implement AsColumnFamilyRef
for Arc<Mutex<BoundColumnFamily<'a>>> to remove this restriction?