ep max evals flag

[xzrderek]

Note

Introduce separate concurrency control for evaluations.

• Add --ep-max-concurrent-evaluations CLI option in plugin.py, normalize it, and export EP_MAX_CONCURRENT_EVALUATIONS
• Implement parse_ep_max_concurrent_evaluations and use it in evaluation_test to set max_concurrent_evaluations
• Thread max_concurrent_evaluations through evaluation_test (including priority scheduler) and EPParameters
• Minor variable naming cleanup for rollout concurrency parsing

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