[Bug] package is missing py.typed

[phelps-sg]

What happened?

the api has type annotations, but there is no py.typed file so consumers cannot check types when calling the package

Steps to reproduce

1. Add dspy as a dep to a project
2. copy and paste one of the examples into the project
3. configure the project to use mypy
4. run mypy

 error: Cannot find implementation or library stub for module named "dspy"  [import-not-found]

DSPy version

3.0.3