Tweak `valence_nbt` (#430) #1349

Job	Run time
valence-fmt (ubuntu-latest, default, nightly-2023-06-20)	29s
valence-tests (windows-latest, default, stable)	30m 39s
valence-tests (macos-latest, default, stable)	23m 46s
valence-tests (ubuntu-latest, default, stable)	15m 6s
extractor-tests (windows-latest)	4m 38s
extractor-tests (macos-latest)	2m 59s
extractor-tests (ubuntu-latest)	2m 27s
valence-clippy (windows-latest, default, stable)	17m 42s
valence-clippy (macos-latest, default, stable)	8m 52s
valence-clippy (ubuntu-latest, default, stable)	5m 50s
valence-docs (windows-latest, default, stable)	13m 51s
valence-docs (macos-latest, default, stable)	9m 1s
valence-docs (ubuntu-latest, default, stable)	4m 40s
	2h 20m 0s

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