Granular error checking during vcJwt verify call

[nitro-neal]

We need to have an ability to check which error happened in our test vectors, only having errors:true could lead to false positives, eg its failing for a different reason than you think

instead of having error messages in our test vector:

      "errorMessage":{
        "web5-js":"Verification failed: Malformed JWT. expected 3 parts. got 2",
        "web5-kt":"Malformed JWT. Expected 3 parts, got 2"
     }

Lets come up with a new way to have more grainular error testing. Probably something like this:

   "errorType": "InvalidSignature"

more context here - https://github.com/TBD54566975/web5-spec/pull/146

[jiyoontbd]

Also consider adding unit tests that check error messages, without depending on test vectors to tell you the expected error message