Fix stream encoder tail buffering #153

Job	Run time
Miri	12m 38s
Format, lint, test, and audit	1m 6s
Platform tests (macos-latest)	31s
Platform tests (ubuntu-latest)	22s
Platform tests (windows-latest)	51s
no_std target build (wasm32-unknown-unknown)	20s
no_std target build (aarch64-unknown-linux-gnu)	19s
no_std target build (thumbv7em-none-eabihf)	16s
no_std target build (x86_64-unknown-linux-gnu)	15s
no_std target build (x86_64-unknown-freebsd)	19s
	16m 57s

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