build time improvement

[varshith15]

• this PR adds the idea on timing cache which improves the build times significantly
• with timing cache UNet tensorrt compilation takes 70 sec, controlnet takes 25 sec and vae encoder/decoder 1.5 sec
• the timing cache file is the same for all models, it basically keep note of fastest kernel for exact requirement
  for instance: conv2d for shape 128 x 128 -- this doesnt need to searched for again as we have cache

[victorges]

So we add a default value for the timing cache but if it's not created by something else we don't use it? Can you add instructions on how to use this timing cache? Ideally it should be completely transparent to the lib user (incl creating the cache and maybe not leaving any dangling files behind?)