Class for B-Tree nodes
$id : integer
Storage for id of a B-Tree node
$is_leaf : boolean
Flag for checking if node is a leaf node or internal node
$count : integer
Storage for keeping track of node ids
$keys : array
Storage for key-value pairs in a B-Tree node
$links : array
Storage for links to child nodes in a B-Tree node
__construct()
Creates and initializes an empty leaf node with id -1