feat: Principal class serializes to JSON

[krpeacock]

Description

JSON.stringify(principal) currently uses Uint8Array encoding instead of toString. Adding the toJSON method resolves this

How Has This Been Tested?

new unit tests

Checklist:

• My changes follow the guidelines in CONTRIBUTING.md.
• The title of this PR complies with Conventional Commits.
• I have edited the CHANGELOG accordingly.
• I have made corresponding changes to the documentation.

[github-actions]

size-limit report 📦

Path	Size
@dfinity/agent	87.38 KB (+0.01% 🔺)
@dfinity/candid	13.52 KB (+0.05% 🔺)
@dfinity/principal	5.16 KB (+0.12% 🔺)
@dfinity/auth-client	92.55 KB (+0.01% 🔺)
@dfinity/assets	89.96 KB (+0.01% 🔺)
@dfinity/identity	89.82 KB (+0.01% 🔺)
@dfinity/identity-secp256k1	232.51 KB (+0.01% 🔺)

[peterpeterparker]

Isn't this a bit weak? It means that any string is either a principal or a string which can be quite error prone if you stringify and parse an object that contains string and principals.

In @dfinity/utils we prefix principal to make their encoding and decoding more safe by using JSON reviver and replacer.

https://github.com/dfinity/ic-js/blob/main/packages/utils/src/utils/json.utils.ts

[krpeacock]

We could serialize into { "__principal__": principal.toText() } instead. The main case I wanted to cover was just ensuring that JSON.stringify() on objects containing principals handles the case gracefully