The default value of 'precision' in Fabric() should be '32-true'

[shihaoyin]

Bug description

The default value of 'precision' in Fabric() should be '32-true', because it crash when using CLI (precision=16 ).

What version are you seeing the problem on?

master

How to reproduce the bug

fabric = Fabric()

# lightning run model train.py --precision=16
# ERROR: Your code has `Fabric(precision=None, ...)` but it conflicts with the value `--precision=16` set through the CLI.

Error messages and logs

# Error messages and logs here please

Environment

Current environment

#- Lightning Component (e.g. Trainer, LightningModule, LightningApp, LightningWork, LightningFlow):
#- PyTorch Lightning Version (e.g., 1.5.0):
#- Lightning App Version (e.g., 0.5.2):
#- PyTorch Version (e.g., 2.0):
#- Python version (e.g., 3.9):
#- OS (e.g., Linux):
#- CUDA/cuDNN version:
#- GPU models and configuration:
#- How you installed Lightning(`conda`, `pip`, source):
#- Running environment of LightningApp (e.g. local, cloud):

More info

No response

[carmocca]

Hi! Thanks for reporting this. I believe #18928 should fix this