Prevent Duplicates

Currently the "question selector" will check that the problem is not the same as the previous one and pick a new one if that's the case.

Need to improve this that in any set of questions we don't get duplicates if at all possible. If we create a collection of all possible questions and then remove them from the quorum once they are asked this should work. There are some nuances here though:

• What if there are few questions available in the quorum than questions that are going to be asked. If this is the case then once the last question from the quorum is asked then the quorum should be repopulated with the full set of questions to start again.
• What about question weighting. In higher letters we increase the probability of those questions being asked by increasing their number in the quorum. We'll need to deduplicate the questions and provide them ranges of values in which to be selected.

Start by locating the question selector and the quorum construction, then read the existing previous-question check and weighting logic. The work is done when a set avoids duplicates where possible, repopulates after the available questions are exhausted, and preserves weighted selection through deduplicated ranges.