refactor: add a `py.typed` marker file to `pulseengine/` to declare the package as PEP 561 typed

[Codex-Crusader]

Summary

The pulseengine/ package uses type annotations throughout but is missing the py.typed marker file required by PEP 561 to signal to type checkers (mypy, pyright, pylance) that the package exports typed stubs.

Without this file, downstream tools and IDEs that import pulseengine as a library dependency will treat it as untyped, ignoring all the careful annotations in the codebase.

Fix

Create an empty pulseengine/py.typed marker file:

touch pulseengine/py.typed

Also update pyproject.toml (if one is added in the future) or note this in CONTRIBUTING.md under the typing section.

Related

This is a zero-code-change fix that dramatically improves the developer experience for anyone who imports from pulseengine.core in a typed project or uses an IDE with pyright/pylance enabled.