[Refactor] Update node IDs from local to global

[Pabloo22]

The JobShopGraph is moving from global node IDs to type-based ones (see #31).

Node

• Change Node class type hint from int to a tuple of node type as a string and the local ID (tuple[str, int]).
• Update documentation to reflect this change

JobShopGraph

Update node ID handling:

• Refactor _next_node_id to be a dictionary pointing each node type to its next node id (dict[str, int])
• Update add_node method to reflect this new behaviour.
• Do the same with removed_nodes attribute and remove_node method
• Update documentation to reflect this change

Checks

• Refactor old tests in the graph module to account for this new behaviour. Tests related to the SingleJobShopGraphEnv may not pass, but that will be addressed in a separate issue. Also, ensure that the visualisation functions plot_disjunctive_graph and plot_resource_task_graph don't break.