feat: add `to_string` method to `SparkLikeExprDateTimeNamespace` #6015

Job	Run time
pytest-38 (3.8, windows-latest)	1m 47s
pytest-full-coverage (3.11, ubuntu-latest)	4m 42s
pytest-38 (3.8, ubuntu-latest)	50s
pytest-full-coverage (3.13, ubuntu-latest)	2m 53s
pytest-windows (3.10, windows-latest)	11m 40s
pytest-windows (3.12, windows-latest)	3m 37s
	25m 29s

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