[xdoctest][task 109] Reformat example code with google style in pytho…

…n/paddle/optimizer/lr.py (#56225)

* [xdoctest][task 109] test=docs_preview

* fix whitespace test=docs_preview

* Apply suggestions from code review

* fix indent and legacy fluid apis

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Co-authored-by: Nyakku Shigure <[email protected]>