Add: ST40 ANC split-packet and interlaced mode

[moleksy]

APIs: Interlaced flag now flows through TX pipeline creation instead of being rejected.

APIs: extend ST40 API/pipeline headers with split-ANC flag, test-pattern config (no-marker/seq-gap/bad-parity/paced), and richer frame-info (marker, seq_discont, seq_lost, per-port pkt counts) so apps and plugins can drive and observe negative/edge scenarios.

Pipeline core: TX gains split-ANC packetization, test mutations (seq gaps, parity corruption, paced inter-packet timing, marker suppression), and pacing adjustments; RX tracks in-flight frames, marker detection, seq gaps/loss, per-port packet counts, and readies frames at timestamp boundaries. Frame buffers reset these fields consistently.

GStreamer plugins: ST40P TX header carries interlaced/split/test fields; RX/TX plumbing maps new flags/test configs into transport.

Validation harness: GstreamerApp supports interlaced flag plumbing, split-anc, test-mode knobs, frame-info paths/ring-size, file-compare suppression, interlace mismatch detection, and frame-info summarization/logging; compare_files can suppress fail logs; case-id sanitization trims parametrized suffixes.

Tests (single/dual): ST40 ANC suites now cover interlaced paths, split-by-packet mode, parity corruption, seq gap/loss, missing markers, paced bursts, multi-packet accumulation, and dual-host basics; pacing test asserts RTP tick deltas; frame-info parsing shared utilities added. Dual-host smoke enables frame-info logging.

Integration tests: new noctx st40i suite exercises split-ANC interlaced handling, split flag propagation, seq-gap reporting, and loopback.

Tools: add rtp_anc_sender helper to craft split-mode RTP bursts (gap/paced) for manual/automated checks.

Docs: st40_validation_updates.md updated with description details of the new validation coverage; design/validation docs touched accordingly.