feat: add decapsulateCode method

[jacobheun]

This allows users to remove the last index of a given protocol code. It behaves like decapsulate, but checks protocol codes rather than string matching the whole multiaddr.

Unlike decapsulate, decapsulateCode will not throw when the code isn't present, it just returns the original address, because "I did what you asked" is better than "OMG I couldn't find it!!!".

Why?

It's often the case in Libp2p that we want to encapsulate/decapsulate the PeerId in a Multiaddr. This makes it easier to avoid validation problems when using mafmt.

For example, let's say there is a peer at /ip4/127.0.0.1/4001, with an id of QmcgpsyWgH8Y8ajJz1Cu72KnS5uo2Aa2LpzU7kinSupNKC.
Encapsulated they yield, /ip4/127.0.0.1/4001/p2p/QmcgpsyWgH8Y8ajJz1Cu72KnS5uo2Aa2LpzU7kinSupNKC.

If i do a validation check for tcp, it will fail, because p2p is not part of a valid tcp address. Today, we would do addr.decapsulate('p2p') to get the tcp address.

The problem with this is:

1. p2p is the default now, but older versions use ipfs. So any protocol that has a name alias might fail depending on the version of multiaddr being used as the stringified address will be different. In a large ecosystem of modules like IPFS or Libp2p, it's common to have multiple versions of multiaddr as it's used so prevalently.
2. Decapsulate currently matches strings. This is useful when you want to decapsulate more complex addresses. However, this will cause problems decapsulating protocols from complex addresses.
   An address like /ip4/0.0.0.0/tcp/8080/p2p/QmZR5a9AAXGqQF2ADqoDdGS8zvqv8n3Pag6TDDnTNMcFW6/p2p-circuit would result in only /p2p-circuit being removed, instead of the actual p2p protocol.