GH-42018: Add numpy.StringDType support #54901

Job	Run time
AMD64 Windows 2022 Python 3.13	5m 12s
ARM64 macOS 14 Python 3	4m 56s
AMD64 macOS 15-intel Python 3	10m 8s
AMD64 Conda Python 3.11 Without Pandas	3m 28s
AMD64 Conda Python 3.10 Pandas 1.3.4	9m 30s
AMD64 Conda Python 3.10 Sphinx & Numpydoc	14m 54s
AMD64 Conda Python 3.13 Pandas latest	3m 57s
AMD64 Conda Python 3.12 without NumPy	3m 39s
	55m 44s

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