[ci] [python-package] add more linting checks

[jameslamb]

Proposes adding a few more linting rules for Python code in this project, to further standardize how the code looks.

• flake8-print: encourages the use of the configured logger over print() and pprint()
• flake8-return (just one of the checks): avoid unnecessary assignment immediately before a return()
• flake8-simplify (just one of the checks): use dict.get(key. default) instead of an if-else loop

This PR adds those checks to the project's linting config, and modifies the project's code to address these specific warnings:

python-package/lightgbm/basic.py:129:9: T201 `print` found
python-package/lightgbm/basic.py:474:16: RET504 [*] Unnecessary assignment to `aliases` before `return` statement
python-package/lightgbm/basic.py:3213:16: RET504 [*] Unnecessary assignment to `booster` before `return` statement
python-package/lightgbm/plotting.py:737:12: RET504 [*] Unnecessary assignment to `graph` before `return` statement
python-package/lightgbm/plotting.py:696:5: SIM401 [*] Use `feature_names = model.get('feature_names', None)` instead of an `if` block
tests/distributed/_test_distributed.py:28:12: RET504 [*] Unnecessary assignment to `port` before `return` statement
tests/distributed/_test_distributed.py:51:12: RET504 [*] Unnecessary assignment to `dataset` before `return` statement
tests/distributed/_test_distributed.py:153:16: RET504 [*] Unnecessary assignment to `y_pred` before `return` statement
tests/python_package_test/test_engine.py:1724:12: RET504 [*] Unnecessary assignment to `trainset` before `return` statement
tests/python_package_test/utils.py:195:12: RET504 [*] Unnecessary assignment to `obj_from_disk` before `return` statement

Docs for these checks can be found at https://beta.ruff.rs/docs/rules.

[github-actions]

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