Properly annotate types on `ts`, `Node`, `Edge`, and `Struct` types so that autocompletion and intellisense tools work correctly

[timkpaine]

csp nodes and graphs are type-annotated to return ts["T"], and are then connected to other nodes/graphs. Additionally, the return value of these ts["T"] which is an Edge, has a number of of convenience methods such as those in https://github.com/Point72/csp/issues/40, a number of operators, and more to come including those in https://github.com/Point72/csp/pull/60. Finally, csp.Struct is statically typed and should integrate properly in intellisense tools.

We should look to the tools themselves to see how to best integrate: https://github.com/microsoft/vscode-python/issues/2446 https://github.com/microsoft/python-language-server/issues/260