fix(artifacts): remove run creation for artifact downloads if not using core

[ibindlish]

Description

• Fixes WB-16643

What does the PR do?

Run creation was made a part of artifacts downloads to communicate with the wandb core process. Since artifact downloads are not a part of the python core, we can avoid run creation unless users install and wish to use wandb-core. In the future, instead of creating a run, we will explore using streams to communicate with the core.

Testing

api = wandb.Api()
artifact = api.artifact('test-paige/uncategorized/b2:v0')
path = artifact.download()

tested and verified that runs are created only if wandb-core is installed

[codecov]

Codecov Report

Merging #6746 (135f4b3) into main (0f9d8dd) will decrease coverage by 0.02%.
The diff coverage is 81.81%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6746      +/-   ##
==========================================
- Coverage   79.45%   79.43%   -0.02%     
==========================================
  Files         447      447              
  Lines       49558    49557       -1     
==========================================
- Hits        39376    39367       -9     
- Misses       9936     9945       +9     
+ Partials      246      245       -1     

Flag	Coverage Δ
func	52.12% <13.63%> (-0.01%)	⬇️
system	63.66% <81.81%> (-0.27%)	⬇️
unit	58.86% <4.54%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
wandb/sdk/artifacts/artifact.py	92.51% <81.81%> (-0.01%)	⬇️

... and 17 files with indirect coverage changes