Conditional import for transformers

[sammer1107]

Use conditional import for transformer module in logging.py

Only import and configure the logging of the transformer module only if it exists.
This allows the user not to install the nn components when using only linear models.

Test CLI & API (bash tests/autotest.sh)

• Test Pass
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• Not Applicable (i.e., the PR does not include API changes.)

Test quickstart & API (bash tests/docs/test_examples.sh)

• Test Pass
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Check API Document

• API document is updated (linear, nn)
• Not Applicable (i.e., the PR does not include API changes.)