feat(syntonia): UV-5R EEPROM memory map + channel codec

[forkwright]

Summary

• BCD frequency codec (lbcd4 encode/decode) with 10 Hz step resolution
• Tone codec mapping ul16 values to CTCSS/DCS/None with full 104-code DCS table
• Channel encode/decode with full bit field handling (power, bandwidth, scan, BCL)
• Memory map constants for all UV-5R EEPROM regions
• MemoryImage type with bounds-checked slice/write access
• Plan-level decode_all_channels / encode_all_channels
• Round-trip tested: decode → encode produces identical bytes
• 42 baofeng-specific tests covering all codecs

Test plan

• cargo build && cargo test --workspace
• cargo clippy --workspace --all-targets -- -D warnings
• cargo fmt --all -- --check
• BCD round-trip on known frequencies (146.520, 446.000, 462.5625 MHz)
• Tone round-trip for all 50 CTCSS + 104 DCS codes (both polarities)
• Channel decode/encode round-trip with fixture image
• Byte-level round-trip: decode → encode produces identical bytes

🤖 Generated with Claude Code

[github-actions]

⚠️ Large PR detected — 18 files, 2426 lines changed.

Consider splitting into smaller PRs for easier review. Not a blocker, just a signal.