Decode signature from assertion response

[broody]

AuthenticatorAssertionResponse expects the signature to be raw ECDSA, however, what's returned from authenticator is DER encoded ECDSA. This PR just decodes it and returns raw signature.

*Marking as draft until audit is done

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 63.70%. Comparing base (fd2336f) to head (8618af7).
Report is 1 commits behind head on main.

Files	Patch %	Lines
.../account_sdk/src/webauthn_signer/signers/device.rs	0.00%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #56      +/-   ##
==========================================
- Coverage   64.14%   63.70%   -0.44%     
==========================================
  Files          16       16              
  Lines        1163     1171       +8     
==========================================
  Hits          746      746              
- Misses        417      425       +8     

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