[#470] Unpacking of right-combed pairs

Description

This MR updates the unpacking logic to handle the 2 new binary representations for right-combed pairs (introduced in edo, more details here).

Because the Micheline decoding logic is implemented using the unpacking logic, we can now parse the 2 new Micheline representations as well.

Examples of the new Micheline representation:

$ tezos-client convert data 'Pair 1 2 3' from michelson to json --type 'pair int int int'
{ "prim": "Pair",
  "args": [ { "int": "1" }, { "int": "2" }, { "int": "3" } ] }

$ tezos-client convert data '{1 ; 2 ; 3}' from michelson to json --type 'pair int int int'
[ { "int": "1" }, { "int": "2" }, { "int": "3" } ]

For comparison, here's the "normal" notation:

$ tezos-client convert data 'Pair 1 (Pair 2 3)' from michelson to json --type 'pair int int int'
{ "prim": "Pair",
  "args":
    [ { "int": "1" },
      { "prim": "Pair", "args": [ { "int": "2" }, { "int": "3" } ] } ] }

Related issue(s)

Resolves part of #470 (closed)

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