test: add unit tests for parse_action and action helpers

[nankingjing]

Summary

This PR adds the first unit tests to the repository. Currently there are zero tests despite pytest being listed as a dev dependency in setup.py.

What is tested

tests/test_handler.py covers phone_agent/actions/handler.py:

• do(...) actions: Tap, Launch, Swipe, Back, Double Tap, Wait, and Tap with a confirmation message
• Type / Type_Name actions: the special-cased text-extraction path (including spaces, special characters, and Type_Name normalization to Type)
• finish(...) actions: message extraction
• Error handling: empty string, unknown action prefix, and garbage input all raise ValueError
• Helper constructors: do() and finish() metadata injection

All tests are pure and deterministic — no device (ADB/HDC/WDA) or network access required.

Why this matters

parse_action() is the critical bridge between raw model output and device actions. It is completely deterministic and self-contained, making it the ideal starting point for a test suite. These tests lock in the current parsing contract and guard against regressions when the parser is extended (e.g. for GLM-4.6V box tokens or new action types).

Running

pytest tests/test_handler.py -v