Use dedicated logger instead of the root one

[patricklabatut]

What does this PR do?

This introduces the use of a dedicated logger throughout the library instead of relying on Python's root logger.

Test Plan: CI + local ad-hoc script:

$ ./test_logging.py
2022-10-10 15:20:15,468 WARNING MainThread xformers WARNING:
Need to compile C++ extensions to get sparse attention support. Please run python setup.py build develop

Before submitting

• Did you have fun?
  • Make sure you had fun coding 🙃
• Did you read the contributor guideline?
• Was this discussed/approved via a Github issue? (no need for typos, doc improvements)
  • N/A
• Did you make sure to update the docs?
  • N/A
• Did you write any new necessary tests?
  • N/A
• Did you update the changelog? (if needed)
  • N/A

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

[codecov-commenter]

Codecov Report

Base: 90.39% // Head: 90.58% // Increases project coverage by +0.19% 🎉

Coverage data is based on head (6789c00) compared to base (e31c571).
Patch coverage: 71.69% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #478      +/-   ##
==========================================
+ Coverage   90.39%   90.58%   +0.19%     
==========================================
  Files          76       76              
  Lines        4548     4567      +19     
==========================================
+ Hits         4111     4137      +26     
+ Misses        437      430       -7     

Flag	Coverage Δ
Python	90.58% <71.69%> (+0.19%)	⬆️

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

Impacted Files	Coverage Δ
xformers/__init__.py	52.23% <25.00%> (+0.72%)	⬆️
xformers/triton/softmax.py	92.15% <33.33%> (+0.15%)	⬆️
xformers/components/attention/__init__.py	87.23% <50.00%> (+4.62%)	⬆️
...formers/components/attention/scaled_dot_product.py	95.12% <50.00%> (+0.12%)	⬆️
xformers/components/feedforward/fused_mlp.py	91.66% <50.00%> (+0.36%)	⬆️
xformers/factory/weight_init.py	90.90% <50.00%> (+0.08%)	⬆️
xformers/triton/layer_norm.py	89.06% <50.00%> (+0.17%)	⬆️
xformers/triton/utils.py	93.10% <50.00%> (+3.81%)	⬆️
xformers/factory/block_factory.py	97.05% <66.66%> (+0.02%)	⬆️
xformers/sparse/blocksparse_tensor.py	88.99% <66.66%> (+0.51%)	⬆️
... and 14 more

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[fmassa]

Thanks Patrick!