Add from_jwk to Ed25519Algorithm (Support kty: OKP).

[dajiaji]

See #621.

I have implemented from_jwk() on Ed25519Algorithm to support JWK compliant with RFC8037 and I also added tests for that, achieving 100% test coverage.

I'd appreciate it if you can check and merge it.

Close #621

[jpadilla]

Thanks for taking the time to put this together, really appreciate it! Can you also update the CHANGELOG?

[jpadilla]

TIL: raise... from... is a thing!

[dimaqq]

Actually, automatic exception chaining is a thing since 3.0.
There's only a subtle difference between automatic raise and explicit raise from.

Usually I'd argue for raise from None, however in this case, perhaps, the details of the inner excption are useful, e.g.:

Traceback (most recent call last):
  File "/.../pyjwt/jwt/algorithms.py", line 615, in from_jwk
    return Ed25519PublicKey.from_public_bytes(x)
  File "/.../pyjwt/env/lib/python3.9/site-packages/cryptography/hazmat/primitives/asymmetric/ed25519.py", line 27, in from_public_bytes
    return backend.ed25519_load_public_bytes(data)
  File "/.../pyjwt/env/lib/python3.9/site-packages/cryptography/hazmat/backends/openssl/backend.py", line 2344, in ed25519_load_public_bytes
    raise ValueError("An Ed25519 public key is 32 bytes long")
ValueError: An Ed25519 public key is 32 bytes long

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/.../pyjwt/tests/test_algorithms.py", line 798, in test_ed25519_jwk_fails_on_invalid_json
    algo.from_jwk(v)
  File "/.../pyjwt/jwt/algorithms.py", line 619, in from_jwk
    raise InvalidKeyError("Invalid key parameter") from err
jwt.exceptions.InvalidKeyError: Invalid key parameter

[dajiaji]

@jpadilla Thanks! This update is very useful for me.