feat(devboxes): use optimistic create endpoint

[adam-rl]

Summary

• use the optimistic devbox create endpoint inside sync and async create_and_await_running
• return immediately when the server observes running
• retain the existing long-poll fallback for transitional responses
• keep the raw endpoint out of the generated public API surface

Testing

• Ruff lint and format checks
• mypy on the modified resource
• 14 focused sync/async pytest cases

Depends on runloopai/runloop#10859.