v2.37.0: publish training_gpus_per_agent only on LLM training schemas

Fixes

• publish training_gpus_per_agent only on LLM training schemas

  The published agilerl-arena training-manifest schema now defines training_gpus_per_agent only on the LLM training spec. Classic RL and multi-agent gym algorithms no longer expose that key.

  to_payload() omits it for non-LLM runs, and for LLM runs that leave the default unset.

Other

• merge per-root junit as well-formed XML

  Two-root pytest shards no longer concatenate <testsuites> wrappers with string slicing. The merged junit report is built with ElementTree so duration promote can parse it.

  Cover stripping non-form algorithm fields from JSON Schema required lists.

• run Linux CPU, ty, and coverage on GitHub-hosted Ubuntu

  Linux CPU pytest, ty, and coverage combine run on ubuntu-24.04 without CUDA torch or vLLM. GPU pytest stays on self-hosted gha-runner-scale-set runners. The llm extra is Hugging Face transformers/PEFT/datasets plus Liger and bitsandbytes on Linux. vLLM lives in the vllm extra. The cpu extra selects CPU-only PyTorch.

Full Changelog: v2.36.2...v2.37.0