chore(auth): add webauthn tests

[mandarini]

Moved from: supabase/auth-js#1127
Author: @Bewinxed

What kind of change does this PR introduce?

Enhancement + Small bug fix
Add tests for the webauthn factorType and its (de)serialization/merging helpers.
Fix fallback naming for the credential when no friendlyname is provided and the username is null

What is the current behavior?

The factorId parameter was being sent in both the URL path and the request body when calling the MFA challenge endpoint, which could cause issues with the API.

No tests for factorType webauthn

What is the new behavior?

• Destructured factorId from params in the _challenge method to only include it in the URL path, not the request body
• Added tests for serialization/deserialization.
• Added WebAuthn helper tests to validate merge operations
• Configured docker-compose.yml with WebAuthn environment variables for local testing

Additional context

We still need to bump the /auth version in the dockor-compose.yml once the build that supports webauthn is out.