CausalProblem rework (#84)

* Reinstate check after renaming caused bugs in sampling

* Remove old CausalProblem class

* Add barebones classes to be populated later

* Update two normal example test to use new infrastructure

* Rework so that the lagrangian can be passed model parameters and the multiplier values as separate args

* ruffing

* Refactor out g.model argument from the Lagrangian call

* Make TODOs obvious so I don't forget to do them

* Add docstrings and more TODOs

* Todo resolution and addition

* Fix module-level placeholder docstrings

* Add issue tags to TODOs

Author: willGraham01

src/causalprog/causal_problem.py

@@ -0,0 +1 @@
+"""Classes for defining causal problems."""