Implement Range Values

[samuelrince]

The main goal of this PR is to add Range object to model intervals. It integrates with Impact data model and can be compared or added with integers and floats.

Added

• Range model
• Tests of Impact models
• Environmental impacts tutorial page

Changed

• Separate compute_llm_impacts function into two functions, compute_llm_impacts_dag that returns raw results and compute_llm_impacts that returns the Impacts model.
• request_latency is now an optional parameter of compute_llm_impacts
• compute_llm_impacts from tracer.utils is now llm_impacts

[adrienbanse]

Thanks @samuelrince, it's good to go for me. Let me just specify the units of the latency in the code so that we can close #49 with this PR.

[adrienbanse]

@samuelrince Ready for merging 🍾