Use sync.Pool for blake3 hashers (#6044) #19172

Job	Run time
filter-changes	8s
lint	4m 11s
quicktests	2m 18s
build-tools (ubuntu-22.04)	2m 1s
build-tools (self-hosted, linux, arm64)	6m 7s
build (ubuntu-22.04)	2m 2s
build-tools (macos-13)	2m 51s
unittests (ubuntu-22.04)	23m 13s
build (self-hosted, linux, arm64)	1m 21s
build-tools (self-hosted, macOS, ARM64, go-spacemesh)	10m 44s
build (macos-13)	3m 24s
unittests (self-hosted, linux, arm64)	28m 34s
build (self-hosted, macOS, ARM64, go-spacemesh)	23s
build-tools (windows-2022)	6m 16s
unittests (macos-13)	29m 48s
build (windows-2022)	6m 7s
unittests (self-hosted, macOS, ARM64, go-spacemesh)	18m 48s
unittests (windows-2022)	31m 58s
ci-status	5s
	3h 0m 19s

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