Fix linking transformers time stamps & include fuel price shock

[jokochems]

This comprises the following:

• The model has trouble with the (obviously changed?) linking transformers timesteps. It used to cut the last value which resulted in an IndexError in model creation. This simple fix resolves this.
• In the course of the ongoing latest pommesdata update, a commodity fuel price shock has been introduced reflecting the price effect of Ukraine war, see https://github.com/pommes-public/pommesdata/pull/43
• Also, the environment.yml file is enhanced and targeted for usage with mambaforge (no anaconda or defaults channel anymore).

[jokochems]

@yannickwerner: Again, here's a very small thing which I'd be happy to be reviewed by you.

[jokochems]

@yannickwerner: I'll go ahead and merge this since I need the latest features in the dev branch. Feel free to review whenever you find the time. We can address your improvements and suggestions in a dedicated pull request. I'll keep that branch for the sake of transparency.