Update proofs in fixtures

[bgins]

Summary

Problem

Fixtures currently include a proof map like:

      "proofs": {
        "bafkreie3bfwr2pxtzphzpspb3plvdrh3obq5yiyibfuuiqj2m3kcrrexpu": "eyJhbGciOiJFZERTQSIsInR5cCI6IkpXVCJ9.eyJhdWQiOiJkaWQ6a2V5Ono2TWtmZkRaQ2tDVFdyZWc4ODY4ZkcxRkdGb2djSmo1WDZQWTkzcFBjV0RuOWJvYiIsImNhcCI6e30sImV4cCI6OTI0NjIxMTIwMCwiaXNzIjoiZGlkOmtleTp6Nk1razg5YkMzSnJWcUtpZTcxWUVjYzVNMVNNVnh1Q2dOeDZ6TFo4U1lKc3hBTGkiLCJuYmYiOjEsInVjdiI6IjAuMTAuMCJ9.qvC6-4agkAxd72ZKNardHy8YHpKGAhz9sbNlWMys0LBoccifGCl-9Yz3bpy4SuosAbWy-W2tc5MGzFCNRmLpAw"
      }

but the ucan-http-bearer-token spec has been updated to put all proofs in a UCAN proof array: https://github.com/ucan-wg/ucan-http-bearer-token#23-example

Impact

The original intuition for proofs in a map no longer applies. In addition, an implementer might incorrectly cache proofs rather than computing their CIDs.

Solution

Present proofs as an array of tokens.