Add ADB wrapper (adb CLI)

## Summary

Add `AdbRunner` class to `Xamarin.Android.Tools.AndroidSdk` to wrap `adb` CLI operations for device management.

## Background

The MAUI DevTools CLI and IDE extensions need to list connected devices, start/stop the ADB server, and query device state. This functionality should live in the shared `android-tools` package.

Reference implementation exists in `android-platform-support` (internal) `Mono.AndroidTools.Adb`.

## Proposed API Surface

`csharp
public class AdbRunner
{
Task> GetDevicesAsync(CancellationToken ct = default);
Task StartServerAsync(CancellationToken ct = default);
Task KillServerAsync(CancellationToken ct = default);
Task WaitForDeviceAsync(string serial, CancellationToken ct = default);
}

public record AndroidDeviceInfo(string Serial, DeviceState State, string? Model, string? Product, TransportType Transport);
public enum DeviceState { Unknown, Offline, Device, NoDevice, Recovery, Sideload, Unauthorized }
public enum TransportType { Unknown, Usb, Emulator }
`

## Consumer

- **MAUI DevTools CLI** (`maui android devices`) — see [MAUI DevTools Spec PR](https://github.com/dotnet/maui/pull/33865)
- VS/VS Code extensions for device picker

## Related

- dotnet/android-tools#271 (SDK bootstrap)
- MAUI DevTools spec §6.8: Shared Libraries & Code Reuse