fix: ensure BodyPartReader.read() returns bytes, not bytearray #16608

Job	Run time
Generate llhttp sources	8s
Pre-Setup global build settings	3s
Linter	57s
Autobahn testsuite (3.14, ubuntu)	10m 18s
Benchmark	11m 26s
Cython coverage (windows)	3m 21s
Cython coverage (ubuntu)	2m 7s
Test (3.10, windows, false)	6m 19s
Test (3.11, Y, ubuntu, false)	5m 32s
Test (3.12, Y, ubuntu, false)	5m 48s
Test (3.11, ubuntu, false)	4m 29s
Test (3.14, ubuntu, false)	5m 19s
Test (3.10, macos, false)	8m 25s
Test (3.13, Y, ubuntu, false)	5m 28s
Test (3.10, ubuntu, false)	4m 36s
Test (3.11, macos, false)	6m 51s
Test (3.12, windows, false)	5m 47s
Test (3.12, ubuntu, false)	4m 47s
Test (3.13, macos, false)	6m 6s
Test (3.13, windows, false)	5m 33s
Test (3.10, Y, ubuntu, false)	5m 48s
Test (3.13, ubuntu, false)	4m 20s
Test (pypy-3.11, Y, ubuntu, false)	8m 59s
Test (3.14, windows, false)	6m 4s
Test (3.14, macos, false)	7m 37s
Test (3.14, Y, ubuntu, false)	5m 58s
Test (ubuntu, 3.14t, false)	3m 46s
Test (3.11, windows, false)	5m 32s
Test (3.12, macos, false)	5m 40s
check	5s
Pre-Deploy	-1s
Build wheels on ${{ matrix.os }} ${{ matrix.qemu }} ${{ matrix.musl }}	0s
Tarball	0s
Deploy	0s
	2h 37m 8s

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