Dict: gather dictionary values straight into a VarBinBuilder #6623

Job	Run time
Python (wheel build)	6m 55s
check-java-publish-build (aarch64-unknown-linux-gnu, runs-on=30583006875/runner=arm64-medium/imag...	1m 54s
check-java-publish-build (x86_64-unknown-linux-gnu, runs-on=30583006875/runner=amd64-medium/image...	52s
Rust publish dry-run	22s
Compat check / compat-test	3m 52s
	13m 55s

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