Release v7: complete Z21 LAN protocol, docs, CI/CD, and tooling

[jaak0b]

Summary

The v7 release of the Z21 client library.

• Protocol completeness — implement all remaining Z21 LAN protocol V1.13 features (CV/POM programming, R-BUS feedback, RailCom, LocoNet gateway, CAN, fast clock, and the zLink booster/decoder/adapter messages) as commands and response handlers, with neutral capability interfaces for programming, feedback, and fast clock. TDD test-first throughout and verified with Stryker mutation testing.
• Documentation — a DocFX site generated from the source XML doc comments: the API reference for the five shippable assemblies plus a short landing/getting-started page, with built-in search. Published to GitHub Pages via the native Actions deployment (nothing committed). The five packable projects also emit XML docs for consumer IntelliSense.
• Versioning & CI/CD — replace GitVersion with Nerdbank.GitVersioning (version.json + git height); split CI (Build.yml: build/test) from CD (Release.yml: publish to NuGet on push to main, with --skip-duplicate).
• Tooling — add the Z21.SmokeTest manual hardware harness.
• Bug fix — UdpTransport now implements IDisposable, so synchronous DI container disposal no longer throws.

Testing

• Unit and Stryker mutation suites green.
• Verified end-to-end against a physical Z21 (firmware 1.43): connect, system info, track power, driving, and turnout switching all work.

Notes

• Merging this PR triggers Release.yml, which packs and publishes all five NuGet packages (Z21, Z21.DependencyInjection, Z21.Autofac, CommandStation.Abstractions, CommandStation.Transport.Udp) at the nbgv-computed 7.0.x version.
• The NuGet API key scope must include the two new CommandStation.* package IDs.
• Documentation publishing requires Settings -> Pages -> Source = "GitHub Actions".

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Code review fixes (commit efe80fa)

A max-effort review of this branch against the LAN protocol spec found and fixed the following.

Correctness

• LocoInfo decode dropped the last function group (F21–F28, and F29–F31 on FW ≥ 1.42 frames) — an off-by-one in the function-byte loop.
• A throwing handler CanHandle or OnBytesReceived subscriber could permanently kill all inbound handling; the dispatcher and the UDP receive loop now contain it.
• The keep-alive timer is now stopped on a lost connection, not only on an explicit DisconnectAsync.
• 28-step speed decode returns 0 instead of throwing KeyNotFoundException on out-of-range wire values.
• The frame reader rejects a DataLen of 0 or above the 1472-byte limit, preventing unbounded buffering on a corrupt length prefix.

Validation & diagnostics

• SetLocoFunction rejects a function index above the 6-bit field (0–63).
• LAN_GET_HWINFO now surfaces the firmware version alongside the hardware type.
• LocoSpeedOutOfRange messages corrected to 14 / 28 / 126.

Cleanup

• Centralised the big-endian address split in IAddressCodec and used it across the four settings commands; renamed the accessory-mode parameter.
• Added a shared length-safe MatchesFrame guard on IZ21ResponseHandler; migrated handlers off try/catch (IndexOutOfRangeException) and removed the tautological XOR checks while keeping the real checksums.
• AccessoryModeResponseHandler now implements IZ21ResponseHandler, so LAN_GET_TURNOUTMODE responses are discovered and dispatched.

All 678 unit tests pass; Debug and Release builds are clean.