feat(adb): add async process runner for executing commands (#4)

[SamratB8]

Summary

Adds a reusable asynchronous process runner to WinDroid.Adb for safely executing external commands.

Changes

• added ProcessRunner
• added structured CommandResult
• launches executables directly without a shell
• passes arguments safely through ProcessStartInfo.ArgumentList
• captures stdout and stderr concurrently
• returns normal and non-zero exit codes
• supports optional timeout
• supports caller cancellation before or after process startup
• terminates the child process tree on timeout or cancellation
• uses bounded cleanup waits
• returns structured startup failures
• observes eventual faults from unfinished output-read tasks

Validation

• Debug build: 0 warnings, 0 errors
• Release build: 0 warnings, 0 errors
• git diff --check: clean
• scratch harness: 20/20 checks passed
• concurrent 100 KB stdout/stderr test passed without deadlock
• pre-cancelled token test confirmed the child process was never started
• no orphaned test processes remained

No ADB command wrappers, adb devices parsing, UI work, dependency-injection setup, logging, or Issue #5 functionality were included.

Closes #4.