Add Python stubs (pyi) to edtlib.

[rruuaanng]

Is your enhancement proposal related to a problem? Please describe.

Some users install edtlib via PyPi for personal project development. By adding stub (.pyi) files, the code completion can be more comprehensive, enhancing the user's development experience.

Describe the solution you'd like

I advocate for adding stubs to the following files:

• edtlib.py
• dtlib.py

Describe alternatives you've considered

Additional context