Add native Samsung Shannon SDM backend

[mbound]

Summary

Adds a native GPL-2.0-or-later Samsung Shannon/Exynos SDM collector adapted from SCAT at pinned commit 361ff551a4fbb30789c46750c00586682a7a9b26.

Native acquisition

• new sixgrok-samsung-sdm / 6grok-samsung-sdm executable
• default /dev/umts_dm0
• SCAT-compatible CONTROL_START/update-period/item selection
• signaling/radio/full curated profiles
• passive and all-items modes
• CONTROL_STOP
• lossless raw capture/replay
• JSONL normalized capture and MessagePack uplink

Framing safety

• native 0x7f / 14-byte SDM header / 0x7e framing
• validates length1 == length2 + 3
• packet size bound
• fragmented read support and resynchronization

Namespace correctness

Native SDM is kept out of historical parser synthetic MIPC ranges 0x2000..0x23ff.
Whole SDM packets use 0x2400 + group; local JSON exposes group/command/direction/radio/timestamp.

Licensing/provenance

• crate/source remains GPL-2.0-or-later
• exact SCAT commit/path provenance in source and THIRD_PARTY.md
• exact SCAT COPYING retained at LICENSES/GPL-2.0-or-later.txt
• verified Git blob SHA d159169d1050894d3ea3b98e1c965c4058208fe1
• core linked under its MIT option
• MediaTek roadmap attribution corrected (SCAT is not the MediaTek source)

Validation

Final branch head 50196eca643011fcf7efee7e9a0cc51dce7465e7
GitHub Actions run 33981460045 passed:

• cargo test --workspace
• cargo build --workspace
• reuse lint
• cargo deny check licenses sources