Enforce private typed module boundary for 7.0.0

[sam0rr]

Summary

• move protocol framing and wire constants into the private _protocol module
• move serial transport and frame synchronization into the private _serial_manager module
• keep the documented package-root API and all sensor behavior unchanged
• declare exact public interfaces for the typed package and its public modules
• remove the old public-looking internal module paths without aliases or compatibility shims
• prepare the forward-only 7.0.0 package metadata
• correct the README toolchain list to reference Ruff and Vulture instead of Black

Impact

The documented imports from xkc_kl200_python remain unchanged. The internal xkc_kl200_python.utils and xkc_kl200_python.serial_manager paths are intentionally removed. The usage guide, configuration guide, examples, and CI already matched the supported API and required no changes.

Validation

• 79 tests pass
• 372/372 source statements covered (100%)
• Ruff formatting and linting pass
• strict mypy passes
• Vulture reports no dead code
• Prettier passes for all Markdown documentation
• source distribution and wheel build successfully
• the wheel contains py.typed, _protocol.py, and _serial_manager.py
• the built wheel embeds the corrected README metadata
• an isolated strict-mypy consumer check against the built wheel passes
• AST comparison confirms the relocated protocol and transport definitions are unchanged
• three independent codex review --base main reviews found no actionable defects on the final commit