stream: handle setEncoding after buffered data #8106

Job	Run time
Build slim tarball	1m 13s
aarch64-linux: Cache V8 build	23s
x86_64-linux: with shared libraries	28m 13s
aarch64-darwin: with shared libraries	28m 14s
x86_64-darwin: with shared libraries	39m 57s
aarch64-linux: with shared openssl-1.1.1w	23m 56s
aarch64-linux: with shared boringssl-0.20260526.0	23m 57s
aarch64-linux: with shared openssl-3.0.20	23m 46s
aarch64-linux: with shared openssl-3.5.6	23m 55s
aarch64-linux: with shared openssl-3.6.2	24m 6s
aarch64-linux: with shared openssl-4.0.0	24m 23s
	4h 2m 3s

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