benchmarker_V2: sdpa_backend handling and level 2 config issue

[Abdennacer-Badaoui]

System Info

Hi @McPatate, @remi-or,

I noticed a few things in BenchmarkConfig:

1. In check_validity, for continuous_batching you check sdpa_backend is not None and then set it to "math", but earlier it’s already set to "flash_attention" if None. The warning says it should be None, but it’s set to "math".

2. Level 3/4 in get_config_by_level generates all configs but ignores "paged|sdpa", which will be included in level 2.

Thanks!