Rust

Improve Signed Extension and Block Decoding Examples/Book #3945

Job	Run time
Cargo fmt	14s
Check documentation and run doc tests	6m 19s
Cargo clippy	4m 5s
Test (Light Client)	4m 27s
Cargo check	5m 35s
Check unused dependencies	17s
Cargo check (WASM)	1m 24s
Test (Native)	10m 14s
Test (Unstable Backend)	9m 24s
Test (WASM)	6m 32s
	48m 31s

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