[#470] Unpacking/decoding of right-combed pair types

Description

This MR adds these two things:

• Ability to parse right-combed types (e.g. pair int nat string) from all 3 formats (binary, micheline, michelson)
• Ability to parse right-combed values (e.g. Pair 1 2 "a") from the michelson format (the other 2 formats were already implemented in !753 (merged))

Related issue(s)

Resolves part of #470 (closed)

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