Light refactor of InferenceParameters class

* Address suggestions from `pylint` to make the code more readable as
	well as add documentation/type hints.
* Added initial, highly targeted unit tests. Including for the
	`inject_proposal` method.
* Consolidated `hit_*` methods into the `check_in_bound` method.
* Made the `{l/u}bs` attributes private and extract them from the
	distribution object on behalf of the user in `add_single_parameter`.

Author: TimothyWillard