add curve and parameters properties to ECDSAKey protocol

[JaapWijnen]

This adds curve and parameter properties to the ECDSAKey protocol and also makes them public (non settable) on the ECDSA.PublicKey and ECDSA.PrivateKey types.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 69.05%. Comparing base (f97e96f) to head (4bebf97).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #143 +/- ## ======================================= Coverage 69.05% 69.05% ======================================= Files 59 59 Lines 1561 1561 ======================================= Hits 1078 1078 Misses 483 483 ``` | [Files](https://app.codecov.io/gh/vapor/jwt-kit/pull/143?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) | Coverage Δ | | |---|---|---| | [Sources/JWTKit/ECDSA/ECDSA.swift](https://app.codecov.io/gh/vapor/jwt-kit/pull/143?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9KV1RLaXQvRUNEU0EvRUNEU0Euc3dpZnQ=) | `86.00% <100.00%> (ø)` | |

[JaapWijnen]

Not sure what's going on with CI here. Any ideas? @ptoffy or @gwynne ?

[ptoffy]

@JaapWijnen yeah looks like this isn't you, the same error is happening all over Vapor repos. There's probably something wrong with GH's CI or similar