Decouple protocol layer from Qt

[joshperry]

This decouples the protocol layer from PyQt5 so it can be imported from headless/CLI contexts without pulling in the GUI toolkit.

Motivation

The protocol layer (keyboard_comm.py, vial_device.py, and friends) implements HID communication and keymap serialization — none of which requires Qt. However, transitive imports of util.py (which imports PyQt5 at the top level) and unlocker.py (a QDialog subclass) made it impossible to from protocol.keyboard_comm import Keyboard without having PyQt5 installed. This blocks use cases like CLI tooling, scripting, and CI/CD integration.

Changes

New file:

• util_base.py — Contains hid_send, MSG_LEN, chunks, find_vial_devices, is_rawhid, pad_for_vibl, and the serial number magic constants. Zero GUI dependencies.

Refactored:

• util.py — Re-exports everything from util_base via from util_base import ..., so all existing GUI code continues to work with no changes.
• protocol/keyboard_comm.py, protocol/tap_dance.py, protocol/combo.py, protocol/key_override.py, protocol/alt_repeat_key.py, protocol/macro.py — Replaced top-level from unlocker import Unlocker with lazy imports inside the methods that actually use it (only triggered when writing QK_BOOT).
• protocol/macro.py — Also made from macro.macro_action_ui import tag_to_action lazy (Qt dependency via QObject).
• vial_device.py — Imports from util_base instead of util.

New test:

• test/test_protocol_gui_free.py — AST-scans the protocol import chain for top-level Qt and GUI module imports. Catches regressions automatically.

What this does NOT change

• No behavioral changes. The GUI works exactly as before.
• The Unlocker unlock flow is unchanged; it's just imported at call time rather than module load time.
• All existing from util import ... statements in GUI code continue to work via re-export.