perf: remove dtype + fill val handling per chunk #345

Job	Run time
build sdist	18s
build on linux (aarch64 - 2_28)	7m 22s
build on macos (aarch64)	6m 12s
build on linux (armv7 - 2_28)	5m 9s
build on macos (x86_64)	6m 0s
build on linux (x86_64 - 2_28)	5m 30s
build on linux (x86_64 - musllinux_1_2)	5m 7s
build on linux (ppc64le - 2_28)	5m 9s
build on linux (armv7 - musllinux_1_2)	5m 1s
build on linux (aarch64 - musllinux_1_2)	5m 0s
build on windows (x86_64)	13m 3s
inspect	5s
version	0s
publish	0s
	1h 3m 56s

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