Add performance tests

[akrzgc]

This branch is adding performance tests for nanoDFT.

So far it is possible to just execute initial 5 tests with simple purest command purest tests/test_benchmark_performance.py.

The code injecting the ipu_cycle_count into the _nanoDFT() jitted method is WIP.

The branch is going to:

• add nanoDFT() performance evaluation with ipu_cycle_count
• use pytest for performance testing
• add new fullerene molecules such as C80 or C100
• consider using GitHub Action benchmark for performance tracking (either already within this branch or as a separate change)
• refactor the ipu_cycle_count code and move it to utils

[hatemhelal]

An idea to capture the cycle count measurement would be to make it a function decorator. That way we could reuse it outside of nanoDFT as I imagine it would be useful to define micro-benchmarks. I have a preference to break things down into smaller PRs but lets discuss.

[hatemhelal]

I wasn't familiar with these options, looks useful!