feat(adb): add adb devices command wrapper (#5)

[SamratB8]

Summary

Adds a thin adb devices command wrapper to WinDroid.Adb.

Changes

• added AdbDeviceService
• added GetDevicesAsync
• uses the existing ProcessRunner
• accepts a caller-supplied resolved ADB path
• passes exactly one argument: devices
• forwards timeout and cancellation unchanged
• returns the raw CommandResult unchanged

Validation

• Debug build: 0 warnings, 0 errors
• Release build: 0 warnings, 0 errors
• git diff --check: clean
• scratch harness: 14/14 checks passed
• fake ADB confirmed the exact argument list was ["devices"]
• stdout and stderr were preserved verbatim
• timeout, cancellation, startup failure, and non-zero exits flowed through unchanged

No device parsing, device models, UI work, dependency-injection registration, retries, logging, or Issue #6 behavior were included.

Closes #5.