* support cuda virtual devices
* disable NCCL path when virtual devices are used
* label virtual devices in description; add GPUx2 server CI jobs
* code refactor
* fix NemotronH vocab loading by using trust_remote_code for unsupported config patterns
* fix NemotronH tokenizer loading by overriding set_vocab with trust_remote_code
* flash attention support for head dimension 512 added
* FA D=512 - match 576 configs, limit ncols2, revert vec cap
* fix HIP tile kernel build for D=512
* fix HIP tile kernel occupancy for D=512 on AMD
* Apply suggestions from code review
Co-authored-by: Johannes Gäßler <johannesg@5d6.de>
* fix tile FA compilation
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Co-authored-by: Johannes Gäßler <johannesg@5d6.de>