Detect Fireblocks http timeout error

[ian-shim]

Why are these changes needed?

The http client does not wrap the error but concatenates error strings, which doesn't let the err unwrap.
All errors from the client will be url.Error type which supports Timeout() method to tell whether the request timed out.
This PR uses this method to tell whether the request timed out, instead of unwrapping the error using errors.Is.

See playground here

Checks

• I've made sure the lint is passing in this PR.
• I've made sure the tests are passing. Note that there might be a few flaky tests, in that case, please comment that they are not relevant.
• Testing Strategy
  • Unit tests
  • Integration tests
  • This PR is not tested :(