Support regional energy mixes

[adrienbanse]

For now, we only use the world mix to compute GWP, ADPE and PE:

IF_ELECTRICITY_MIX_GWP = 5.90478e-1     # kgCO2eq / kWh (World)
IF_ELECTRICITY_MIX_ADPE = 7.37708e-8    # kgSbeq / kWh (World)
IF_ELECTRICITY_MIX_PE = 9.988           # MJ / kWh (World)

But we know that some providers only have servers in a specific region (e.g. OpenAI in the US).

We could add a column in data/models.csv indicating a zone (country, continent, ...), and then query another .csv (or query some database in another way) to ask for an average energy mix of the zone, or keep the World mix if unspecified.

[adrienbanse]

If we can query an API such as Electricity Maps, then we can even make it time-dependent.

[adrienbanse]

Started to work on this in feat/variable_mixes

[adrienbanse]

Let's re-start this from scratch, and do the following:

• Make llm_impacts more flexible with electricity mix
• Add initialisation parameters to change the default mix (e.g. Ecologits.init(electricity_mix="USA")) (see Configuration system #57)