84 update base64url encoding

[JohnGuilding]

This PR:

1. Updates the base64url library used in the primitives project based on recent changes to the FCL lib
2. Updates some misleading and incorrect forge tests. They were misleading as they indicated the function under test could validate an incremented nonce. This sort of check is managed by the entry point so we do not need to test such scenarios. Additionally, the nonce increment syntax was wrong as it incremented the nonce after the assertion, not before which was the intended behaviour (pointed out by @jzaki).

What are the changes to the base64url library?

If interested in the details, see the following closed PR into the FCL lib. The TLDR is that the base64url library got updated to be more in-line with the webauthn spec. You can verify the changes made in this PR by comparing Base64Url.sol to the FCL Base64Url.sol file

The webauthn standard specifies that base64url encoding should be used for encoding the client challenge. All trailing '=' characters should also be removed - from the spec:

challenge, of type DOMString
This member contains the base64url encoding of the challenge provided by the Relying Party. See the § 13.4.3 Cryptographic Challenges security consideration.

Base64url encoding
The term Base64url Encoding refers to the base64 encoding using the URL- and filename-safe character set defined in Section 5 of [RFC4648], with all trailing '=' characters omitted (as permitted by Section 3.2) and without the inclusion of any line breaks, whitespace, or other additional characters.