[Perf] Speed up LoRA Batch Initialization

[lifuhuang]

Motivation

prepare_lora_batch is triggered once per forward pass and is one of the main sources of perf overheads from LoRA. Based on suggestion from @Fridge003 , there are some low-hanging fruits for perf optimization such as eliminating unnecessary cuda device syncs.

Current status:

	Baseline	#6960	+ #6994	+ #8940
ITL@P95	78.42 ms	68.24 ms (-13.0%)	52.51 (-33.0%)	38.40 （-51.0%)
ITL@P50	34.36 ms	32.85 ms (-4.4%)	22.68 (-34.0%)	18.30 （-46.7%)
TTFT@P50	91.37 ms	85.52 ms (-6.5%)	62.65 (-31.4%)	53.79 （-41.1%)

• Eliminate unnecessary H2D transfer in set_lora_info (Speed up set_lora_info by eliminating unnecessary H2D transfers #6960)
• Eliminate cuda stream syncs and redundant compute in LoRAManager ([Perf] Refactor LoRAManager to eliminate stream syncs and redundant computations  #6994)
• Experiment torch.compile / cuda grpah for prepare_lora_batch to reduce gaps between kernels (Idea from @hebiao064 , to be verified) (deprioritized as most tensor ops are now moved to server init phase by Improve LoRA Perf by Deprecating FlashInfer and Eliminating Redundant Tensor Ops #8940)

[lifuhuang]

Marking this issue as closed as LoRA batch preparation phase duration has been reduced by over 90% and is no longer the perf bottleneck.