switch boost dependency in bzlmod to bcr #431

Job	Run time
aarch64	1m 2s
arenastring-gcc-stdlibc++-default	39s
arenastring-gcc-stdlibc++-half	40s
arenastring-gcc-stdlibc++-full	43s
basic-gcc-c++20-stdlibc++-asan	49s
basic-gcc-c++20-stdlibc++-tsan	41s
arenastring-clang-stdlibc++-default	41s
basic-gcc-c++14-stdlibc++-asan	46s
arenastring-clang-libc++-default	34s
basic-clang-c++20-stdlibc++-asan	35s
basic-clang-c++20-stdlibc++-tsan	47s
basic-clang-c++20-libc++-asan	35s
cmake	50s
basic-clang-c++20-libc++-tsan	40s
coverage	42s
basic-clang-c++14-stdlibc++-asan	36s
basic-clang-c++14-libc++-asan	41s
cpp14-coroutine	46s
workspace	32s
	13m 19s

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