refactor: Use wait_for predicate to check for interrupt

Also use uint256::ZERO where appropriate for self-documenting code.

src/interfaces/mining.h

@@ -61,7 +61,8 @@ public:
     virtual std::optional<BlockRef> getTip() = 0;
 
     /**
-     * Waits for the tip to change
+     * Waits for the connected tip to change. If the tip was not connected on
+     * startup, this will wait.
      *
      * @param[in] current_tip block hash of the current chain tip. Function waits
      *                        for the chain tip to differ from this.