graph: create GraphT (#166)

* graph: create GraphT

* shorten type display

* re-add 'graph' in arg list

* fix is_connected

* minor doc fixes

* another is_connected fix

* make NodeT bound to Hashable

* a few more type simplifications

* make NodeT a TypeAlias too

* add NodeT to aliases in docs

* add return type doc to is_connected

* remove GraphT from arg doc

* change to full name