Add OP_RETURN and external signature support to builders #6873

Job	Run time
Build target wasm32-wasi	1m 0s
Latest build on ubuntu-latest	40s
Slow Test NU7 on Linux	4m 18s
Slow Test all-pools on Linux	4m 13s
Latest build on macOS-latest	30s
Slow Test Sapling-only on Linux	3m 57s
Slow Test transparent on Linux	4m 6s
Slow Test Orchard on Linux	4m 8s
Test Sapling-only on macOS	3m 1s
Latest build on windows-latest	31s
Test transparent on macOS	3m 7s
Build target thumbv7em-none-eabihf	36s
Test Orchard on macOS	5m 7s
Test NU7 on Windows	13m 12s
Test Orchard on Windows	12m 13s
Check ZFuture build on macOS	1m 29s
Test all-pools on Windows	13m 18s
Test all-pools on macOS	5m 35s
Test Sapling-only on Windows	9m 29s
Check ZFuture build on Linux	22s
Test transparent on Windows	9m 41s
Test Sapling-only on Linux	4m 15s
Test Orchard on Linux	5m 49s
Test NU7 on Linux	6m 31s
Test all-pools on Linux	6m 26s
Code coverage	3h 24m 52s
Bitrot check	1m 8s
Intra-doc links	2m 8s
Rustfmt	14s
protobuf consistency	1m 1s
Check ZFuture build on Windows	1m 19s
Clippy (beta)	1m 10s
UUID validity	4s
Clippy (MSRV)	1m 19s
Test transparent on Linux	4m 30s
Required status checks have passed	3s
	5h 41m 22s

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