Replaces the NotImplementedError stubs AZ-406 reserved on three runner-
side helpers; these were stranded from any tracker ticket since
AZ-407/408 never came back to fill them. Concrete bodies:
* fdr_reader.iter_records: JSONL parser + wire-envelope validator;
recursive *.jsonl walk; projects {schema_version, ts, producer_id,
kind, payload} to runner-side FdrRecord with record_type/monotonic_ms
renames; yields oldest-first.
* frame_source_replay.replay_video: OpenCV VideoCapture decode + JPEG
re-encode; auto-detects file vs directory; injectable sleep_fn for
unit-test pacing.
* imu_replay.ImuReplayer.replay: csv.DictReader parse; degrees->radians
attitude conversion; tolerates scientific notation; same sleep_fn
injection pattern.
Adds 34 unit tests (14 + 10 + 10). Full e2e unit suite: 558 passed (+31).
Existing scenario _harness_helpers_implemented probes still return False
because they also depend on sitl_observer / fc_proxy_runtime stubs that
remain pending; scenario probe cleanup is out of AZ-594 scope.
Co-authored-by: Cursor <cursoragent@cursor.com>
Oleksandr Bezdieniezhnykh