Speedup imports
🚀 Feature
Increase the speed of importing from pytorch_lightning
Motivation
time python -c "from pytorch_lightning import LightningModule"

real    0m3.193s
user    0m1.920s
sys     0m0.557s

vs
time python -c "from torch.nn import Module"

real    0m1.022s
user    0m0.603s
sys     0m0.185s

Note that this difference becomes quite visible when running the following sequence of steps quite often:

load a model (subclass of pl.LighteningModule)
forward pass
close Python interpreter

Pitch
The import speed might be very important for one-off inference usecases.
Alternatives
It is worth mentioning, that I tried to pinpoint a specific module where LighteningModule is implemented and import it from there. However, it did not really change much.
time python -c "from pytorch_lightning.core.lightning import LightningModule"

real    0m3.398s
user    0m2.071s
sys     0m0.597s

I guess I can just get around this issue by clever subclassing and never importing from PL at inference time.
Additional context
Please let me know what your opinions are and whether there is an existing solution that could help me. Thank you in advance