Release 0.3 cleanup

[EthanHeilman]

This PR performs three cleanup needed for release 0.3.

1. Solves the inconsistent naming of boolean flag for turning on GQ Signing. In some places we say SignGQ in other places we say GQSign. We rename such flags to GQSIgn. Fixes: SignGQ and GQSign Confusion #168
2. Renames renames the function which verifies an ID Token from .VerifyProvider(...) to VerifyIDToken(...). I'm normally against renames like this but given that the name of the struct is ProviderVerifier having the function be ProviderVerifier.VerifyProvider(...) costs me 10 minutes doing the wrong thing too many times. Given that the function for verifying a PK Token is VerifyPKToken(...) it seems nature that the function for verifying an ID Token would be VerifyIDToken(...).
3. Deletes unused compatibility function. Release 0.3 will have many breaking changes, it is time to retire client.VerifyPKToken(...) and just use verifier.VerifyPKToken(...)

Tests

• github test https://github.com/openpubkey/gha-test/actions/runs/8573505646/job/23498328408
• gitlab-ci test https://gitlab.com/openpubkey/gl-test/-/pipelines/1241996045
• MFA Cosigner test (on OSX/brave)
• Simple example (os OSX/brave, OSX/firefox, OSX/Safari, OSX/chrome)

[mrjoelkamp]

LGTM