[Core] Faster startup for LoRA enabled models

[Yard1]

This PRs makes the startup time for LoRA models much lower by reusing the CPU dummy LoRA used for memory profiling, which creation time is non-trivial. This doesn't impact any GPU operations/profiling and results in the same measurements being taken.

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[rkooo567]

LGTM. So, this improves the performance because you can just share the underlying tensor when you copy dummy lora right?

[rkooo567]

Add assert self._cached_dummy_lora is not False here?

[Yard1]

that would make caching mandatory

[rkooo567]

oh do we have other use case other than using it for profiling run (which already uses cache)?

[Yard1]

unit testing as well

[Yard1]

@rkooo567 Yes correct, the main issue comes from the fact that creating pinned CPU memory tensors has a large overhead. So we just reuse it.