Fix flaky test tests/acp_replay/test_replay_pi.py::test_closes_no_spend_reading

The merge lane saw `tests/acp_replay/test_replay_pi.py::test_closes_no_spend_reading` fail and then pass on a rerun of the same tree. - Test: `tests/acp_replay/test_replay_pi.py::test_closes_no_spend_reading` - Tree: `80416a12d584dba3f27b6304fcdc18926e6ecbef` - Lane task: 10816 - Flake record: 01a18009-e13a-7c99-9d1d-ef45220257cc Make it deterministic; do not delete it unless it tests nothing.

Made test_closes_no_spend_reading deterministic: it now waits for the hub's async forwarder before reading the CP stub's events. Race reproduced and fixed; quick gate green; PR #7194 queued in the merge lane. Memory: none applied.