Chronik needs to be able to read data from the node. For that, we need to have a reference to `NodeContext`, which we store in `ChronikBridge`. Since for Rust this is an opaque C++ type, we need to pass it around as `std::unique_ptr`.
Eventually, this will be part of the `Chronik` struct so we can access the node when we need, for now this just prints us the tip.
Currently, `ChronikBridge` only exposes `get_chain_tip`.