add list of eco credit measurement units for validation

[technicallyty]

Summary

add a list of valid SI units for credit type validation

Problem Definition

in #428 we implemented credit types as a governance param which include SI units such as kg, ton, etc for each type. It would be nice to validate these parameters with a canonical list of valid SI units

Proposal

add a list of valid SI units similar to below:

• http://qudt.org
• https://github.com/BertVerhees/ucum
• https://ucum.org/trac

if _,ok := validSIUnitMap[creditType.Unit]; ok {
 // yay
}

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For Admin Use

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• Appropriate labels applied
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• Contributor assigned/self-assigned

[ryanchristo]

@aaronc any thoughts on this? Should we include in v4.0 upgrade?

[aaronc]

I would consider this nice to have

[ryanchristo]

I think this might need more consideration. When attempting to write an example for biodiversity, I was not sure how to define the unit and whether that unit would fall under the SI. We also use "metric ton CO2 equivalent" in our current "carbon" credit type. I'm going to move this issue out of our current v4.0 milestone and maybe discuss with Sam before someone picks it up.

[aaronc]

Having on chain validation is probably too restrictive. "metric ton CO2e" is more useful and would fail validation