CI: Use sccache to speed up compilation #5495

Job	Run time
Bitrot check	1m 12s
Latest build on ubuntu-latest	2m 7s
Latest build on windows-latest	4m 56s
Build target wasm32-wasi	1m 3s
Check ZFuture build on Linux	27s
Clippy (MSRV)	1m 17s
Check ZFuture build on macOS	38s
Latest build on macOS-latest	2m 20s
Check ZFuture build on Windows	3m 39s
Clippy (beta)	11s
Code coverage	16m 21s
Intra-doc links	1m 37s
Rustfmt	15s
protobuf consistency	1m 2s
UUID validity	3s
Test on Linux	8m 52s
Test Orchard on Linux	10m 38s
Test NU6 on Linux	8m 49s
Test on macOS	8m 41s
Test Orchard on macOS	11m 50s
Test on Windows	15m 55s
Test Orchard on Windows	18m 28s
Test NU6 on Windows	15m 51s
	2h 16m 12s

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