fix simu gate step 1: cva6.py refactor & collect report

Created by: valentinThomazic

• cva6 refactor & cleanup to enable tandem reports generation for elf tests such as testelf for simu-gate:
  • merge redundant functions to run directed tests in `cva6.py` (`run_c`, `run_elf`, `run_assembly` -> `run_test`)
  • removed broken and unused functions by the way (`run_c_from_dir`, `run_assembly_from_dir`)
• collect sim reports of simu-gate job to display them in the cva6 dashboard : ⚠ the simu gate job will still fail but the result on the dashboard will be accurate and will allow debugging