enable lto for release builds #80

Job	Run time
build-tests	4m 29s
check	2m 18s
build (x86_64-unknown-linux-gnu, ubuntu-latest, true, amd64)	9m 36s
build (armv7-unknown-linux-gnueabihf, ubuntu-latest, true, armv7)	9m 52s
build (aarch64-unknown-linux-gnu, ubuntu-latest, true, arm64)	10m 8s
build (x86_64-apple-darwin, macos-latest)	5m 57s
test (core)	1m 37s
test (rpc)	1m 39s
test (client)	2m 0s
test (engine)	1m 42s
test (daemon)	5m 28s
publish	17s
	55m 3s

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