Async Scheduling Plan

[njhill]

• [AsyncScheduling] Make async overlap work with logprobs #27615
• [BugFix] Handle unscheduled requests properly when async scheduling #27756
• [Core] Async scheduling + structured outputs compatibility #26866
• [BugFix] Fix mixed penalties batch with async scheduling #27910
• [AsyncScheduling] Don't schedule past request max_tokens #27922
• [KV offload] Offloading connector async scheduling support #27648
• [PerfFix] Avoid separate thread for MP executor shm spin #28012 - perf fix for regression in #26866
• [Core] Rework handling of async scheduling config #28250 - ready for review/merge
• [WIP] Enable async scheduling by default #27614 - testing
• [Core] Async Scheduling X Spec Decoding Compatibility #24799 - under review
• Explore Async Scheduling + Pipeline Parallel