blockstore: send duplicate proofs for chained merkle root conflicts #1282

Job	Run time
ios (macos-11, aarch64-apple-ios)	6m 57s
android (ubuntu-20.04, x86_64-linux-android)	3m 0s
ios (macos-11, x86_64-apple-ios)	8m 38s
android (ubuntu-20.04, aarch64-linux-android)	3m 24s
ios (macos-11, aarch64-apple-darwin)	6m 31s
android (ubuntu-20.04, i686-linux-android)	3m 2s
ios (macos-11, x86_64-apple-darwin)	7m 43s
android (ubuntu-20.04, armv7-linux-androideabi)	3m 16s
error_reporting	0s
	42m 31s

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