Add patched examples + tests for different pricing strategies

[alexdewar]

Our example models currently all use the shadow pricing strategy for all SED/SVD commodities and unpriced for OTH commodities, which means the other strategies aren't covered by tests. We should fix this by adding some patched examples with regression tests.

(We can probably skip scarcity, as we're not sure about that one in any case (#677).)

We would also like to have more confidence in the results with different pricing strategies. By creating some patched examples,
it'll make it easier to play around with things.

For the regression tests, it probably makes sense to have separate patched models for the marginal and full cases, to make it easier to figure out which is broken if tests fail.

[alexdewar]

@ahawkes could you possibly give some examples of commodities for which marginal and full-cost strategies would be appropriate? It would be good to make our tests realistic.

[ahawkes]

Gas could be full-cost. Electricity could be marginal cost. (I think that could be done in the simple model)?

If you want something mode complex, then the transport fuels could be full-cost, e.g. in the missing commodity model.

[alexdewar]

Gas could be full-cost. Electricity could be marginal cost. (I think that could be done in the simple model)?

If you want something mode complex, then the transport fuels could be full-cost, e.g. in the missing commodity model.

Great, thank you.