Return a consistent result from signature verification methods

[frankhinek]

Context

At present, signature verification is handled inconsistently across Web5 SDKs:

• JS and Go return a boolean false if a signature isn't valid
• Dart and Kotlin raise an exception

The associated test vectors for ES256K/secp256k1 and Ed25519 indicate that a boolean false should be returned and that no error should be raised/returned.

Work to be done

1. Come to a decision on whether a boolean or error raise should occur when a signature fails the verification check.
2. Update the associated test vectors.
3. Update the SDKs that need to be modified accordingly.
4. Ensure all SDKs pass the test vectors.