removes the vector allocation in shred::merkle::make_merkle_proof (#4… #8969

Job	Run time
ios (macos-13, aarch64-apple-ios)	3m 23s
ios (macos-13, x86_64-apple-ios)	3m 46s
android (ubuntu-20.04, x86_64-linux-android)	2m 13s
android (ubuntu-20.04, aarch64-linux-android)	2m 25s
ios (macos-13, aarch64-apple-darwin)	5m 2s
ios (macos-13, x86_64-apple-darwin)	2m 45s
android (ubuntu-20.04, i686-linux-android)	2m 19s
android (ubuntu-20.04, armv7-linux-androideabi)	2m 27s
error_reporting	0s
	24m 20s

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