Stoichiometry

[qai222]

Is your feature request related to a problem? Please describe.
Record the stoichiometric coefficients of the main chemical equation (assumed following #682) to have a balanced equation.

Describe the solution you'd like
A field at the Compound level. The coefficient should be additive for the same Compound.

1. (without modifying the current schema) convention: for the main chemical equation, the stoichiometric coefficient of a Compound is recorded as a custom CompoundIdentifier whose value is the stringified stoichiometric coefficient.
2. extend Amount.kind to include stoichiometric coefficients.

Describe alternatives you've considered
Something at the Reaction level, ex. a balanced reaction SMILES as a ReactionIdentifier. The problem here is although I can have a balanced equation,

1. I have to have all Compounds identified by SMILES.
2. If the same Compound appears in multiple ReactionInputs, I have no way to know the exact coefficient of one Compound in a specific ReactionInput.

[qai222]

Convention for compound stoichiometry:

• The preferred field for compound stoichiometry is the map Compound.features.
• The key should be "stoichiometric_coefficient" or "stoichiometric_ratio".
• The value should be a Data mesaage with its float_value representing the compound's stoichiometric coefficient or ratio.

(from discussion during OH)