`self.ts.intermediate_inputs_stock` and `self.ts.capital_inputs_stock` behaviour is different for substitutable vs non-substitutable goods.

[sternluke]

self.ts.intermediate_inputs_stock appears to be constant across time for all firms with the exception of firms within the substitution bundle. Intuitively, I would imagine that all firm production and consumption would vary across timesteps. Even if that isn't intended the behaviour, it seems like it should at least be the same for both substituted and non-substituted goods.

self.ts.capital_inputs_stock vary slightly over time but doesn't appear to track firm production or consumption.

As expected, the marked difference in behavour between the substitution and non-substitution bundle goods disappears when substitution is turned off.