Fix leaking login thread in test_login_in_thread_retries_on_failure

[delner]

Problem

Running bundle exec appraisal openai rake test produced intermittent WebMock errors:

#<Thread:... /app/lib/braintrust/state.rb:151 run> terminated with exception
WebMock::NetConnectNotAllowedError: Real HTTP connections are disabled

Cause

test_login_in_thread_retries_on_failure created State.new before setting up WebMock stubs. Since State.new immediately spawns a background login thread when no org_id is provided, the thread attempted HTTP requests before stubs were ready.

Solution

Reorder the test to set up stubs before creating State.new, ensuring the background thread spawns with stubs already in place. This follows the same pattern as PR #65.