rename fetch_key_packages to get_identity_updates

[insipx]

Closes #62

closes #61

Sorry for combining, I thought they were similar enough and forgot 62 was an issue. 61 would have been quite small -- I can split up to make the PRs even smaller if requested

• rename fetch_key_packages & related structs to get_identity_updates.
• add timestamp to return of get_identity_updates
• add regex in integration tests for checking did_urls with timestamp
• generally integration tests need to use Bytes::from_hex

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.36%. Comparing base (2f93b91) to head (54a68d3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #75      +/-   ##
==========================================
+ Coverage   78.75%   79.36%   +0.60%     
==========================================
  Files          14       14              
  Lines         579      596      +17     
==========================================
+ Hits          456      473      +17     
  Misses        123      123              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.