docs: better docs for `Encode` and `Decode` #675

Job	Run time
Build C++ integration example	1m 29s
Build starknet-curve features	19s
Build starknet-crypto features	33s
Build starknet-core features	1m 5s
Build starknet-providers features	1m 13s
Build starknet-signers features	1m 1s
Build starknet-accounts features	53s
Build starknet-contract features	54s
Build starknet-macros features	34s
Build starknet features	1m 53s
	9m 54s

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