Reshape get_ton_equivalent and Absorber_project_carbon

[julienbrs]

Description

In Cpv3, get_ton_equivalent and Absorber_project_carbon (formerly called project_value in Cpv2) have different usages compared to their previous versions.

• Should we keep these functions as they are or adapt them?

Additional context

get_ton_equivalent:

• This function might be utilized for better interoperability across various types of projects, not limited to carbon credits.
• It converts different units to ton equivalent, which could enhance the system's versatility.

Absorber_project_carbon:

• Currently, it represents the total absorption of the project in grams.
• It is a storage variable that should be updated during a rebase.
• It might be more effective as a view getter, calculated from the sum supply of vintages.