docs: better docs for `Encode` and `Decode` #672

Job	Run time
Build C++ integration example	1m 10s
Build starknet-curve features	14s
Build starknet-crypto features	37s
Build starknet-core features	1m 4s
Build starknet-providers features	1m 11s
Build starknet-signers features	51s
Build starknet-accounts features	51s
Build starknet-contract features	52s
Build starknet-macros features	33s
Build starknet features	1m 47s
	9m 10s

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