Expose valid chars & support for multi-byte chars #39

Job	Run time
build-github-hosted (ubuntu-latest, 3.7)	13s
build-github-hosted (ubuntu-latest, 3.8)	12s
build-self-hosted (rpi3-32)	27s
build-github-hosted (ubuntu-latest, 3.9)	12s
build-self-hosted (rpi3-64)	32s
build-github-hosted (ubuntu-latest, 3.10)	13s
build-self-hosted (rpi4-32)	19s
build-github-hosted (windows-latest, 3.7)	44s
build-self-hosted (rpi4-64)	18s
build-github-hosted (windows-latest, 3.8)	39s
build-self-hosted (rpi5-64)	12s
build-github-hosted (windows-latest, 3.9)	39s
build-self-hosted (jetson)	31s
build-github-hosted (windows-latest, 3.10)	22s
build-github-hosted (macos-latest, 3.7)	16s
build-github-hosted (macos-latest, 3.8)	15s
build-github-hosted (macos-latest, 3.9)	21s
build-github-hosted (macos-latest, 3.10)	15s
	6m 40s

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