Consultation about TCI_ratio in uncertainty analysis

a) Hello, as for the setting of ```TCI_ratio```, it seems that it only applies to the unit created using the ```cost decorator``` (https://github.com/BioSTEAMDevelopmentGroup/Bioindustrial-Park/blob/master/biorefineries/lactic/models.py#L251-L258). Why does the cost of other units (such as ```bst.units.Pump, bst.units.HXutility, bst.units.Flash```) remain unchanged in uncertainty analysis?

b) For ```BatchCrystallizer```, the code I use is ```BC101 = bst.units.BatchCrystallizer('BC101', inlet, outlet, tau=24, V=3000, T=30 + 273.15)```,
but why does the following code return ```None```, which causes an error (```TypeError: unsupported operand type(s) for /=: 'NoneType' and 'int'```) when running the code ```unit.cost_items[item].cost /= old_ratio``` (https://github.com/BioSTEAMDevelopmentGroup/Bioindustrial-Park/blob/master/biorefineries/lactic/models.py#L251-L258)?
The code is as follows:
```
import biosteam as bst
from biorefineries import cellulosic
cs = cellulosic.Biorefinery('corn stover ethanol')
inlet = cs.cornstover
BC101 = bst.units.BatchCrystallizer('BC101', inlet, 'outlet', tau=24, V=3000, T=30 + 273.15)
for item in BC101.cost_items:
print(BC101.cost_items[item].cost)
```

Start with biorefineries/lactic/models.py at lines 251-258, then reproduce the provided BatchCrystallizer example and inspect BC101.cost_items. Compare how TCI_ratio is applied to decorated and standard units, and determine why a cost value is None; done means the two reported behaviors are explained and the appropriate follow-up is identified.

Written by the indexing model from the issue text.