FSST: decompress straight into the builder's byte storage #6754

Job	Run time
Rust publish dry-run	30s
Python (wheel build)	6m 30s
check-java-publish-build (x86_64-unknown-linux-gnu, runs-on=30654177660/runner=amd64-medium/image...	56s
Compat check / compat-test	1m 18s
check-java-publish-build (aarch64-unknown-linux-gnu, runs-on=30654177660/runner=arm64-medium/imag...	2m 0s
	11m 14s

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