fix: peer-id privKey and pubKey can be undefined

[nazarhussain]

In the PR #107 the PeerId interface was introduced. Later in the PR #111 that was refactored and some intentional changes introduced.

The privKey and pubKey both can be undefined depending on the data, more details can be found in the PR libp2p/js-peer-id#150.

The PeerId object can be created with the following scenarios:

1. new in that case both keys are optional
2. PeerId.create in that case if provided input is valid than both keys exists
3. PeerId.createFromBytes, PeerId.createFromB58String, PeerId.createFromHexString, PeerId.createFromCID in these cases public key can be decoded but private key don't exists
4. PeerId.createFromPubKey in that case public key exists but not private
5. PeerId.createFromPrivKey in that case both keys exist
6. PeerId.createFromJSON in that case both keys exist
7. PeerId.createFromProtobuf in that case both keys exist

Considering all the above cases, both privKey and pubKey were initially set was set to have undefined values. Seems the change in refactoring PR #111 was made unintended.

[achingbrain]

TLDR: please use the v2.x.x release for the time being, tagged latest on npm - PRs can target the release/v2.x.x branch.

---

Longer version:

The typescript version of libp2p-interfaces is trying to take the interface definitions in a new direction. For peer id, please see the changes in #117 - it makes peer ids essentially a place to store some Uint8Arrays which you can then use to do encryption rather than pulling in libp2p-crypto by default. This is to allow using peer id datatypes in lightweight clients like ipfs-http-client instead of having everything as opaque strings.

It's all a bit in flux and will be until libp2p/js-libp2p#1021 lands.

[nazarhussain]

@achingbrain Please review.

[achingbrain]

Good catch - thanks! Just a few changes needed in order for the tests to not cause unhanded promise rejections if they fail.