Add trajectory polling and move modules

[munrojm]

• Add polling utilities for similarity trajectory data (iter_poll_trajectory, aiter_poll_trajectory, start_polling_trajectory_thread,
  start_polling_trajectory_task)
• Move SimilarityTrajectoryProvider from timeseries/similarity.py to new similarity/ module
• Extract shared drift_corrected_sleep helper to _polling_utils.py for reuse
• Export polling functions from timeseries/__init__.py
• Default stop condition: polls until trajectory is no longer active (not df["Active"].any())
• Add comprehensive tests for trajectory polling (sync, async, thread, task variants)