The pool tests were written with `inlineCallbacks`; trial runs `async`
test methods directly, so use `await`. Adds a test that `txn_limit`
replaces the pooled connection after the configured number of checkouts.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ULdieJyQoHNzeHq42H2M1p