docs: better docs for `Encode` and `Decode` #676

Job	Run time
Build C++ integration example	1m 7s
Build starknet-curve features	14s
Build starknet-crypto features	32s
Build starknet-core features	1m 14s
Build starknet-providers features	1m 21s
Build starknet-signers features	55s
Build starknet-accounts features	49s
Build starknet-contract features	51s
Build starknet-macros features	36s
Build starknet features	1m 53s
	9m 32s

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