feat: use jwtoxide for app attest jwt decoding

[noahpodgurski]

What's new

• Jwtoxide decoding is an almost 50% performance improvement to normal jwt decoding. Replacing jwt decoding in utils.py for app attest processes
• For FxA, if we also want to add this there, best solution might be to fork the repo and include that, or just include the code directly inside the src/ directory, and make those changes there to support jwtoxide. See feat: add pyfxa and override to use jwtoxide #58 to view necessary changes