[FLINK-39578][python] Include py.typed in PyFlink distribution

[florianvazelle]

What is the purpose of the change

This pull request ensures that the py.typed marker file is included in the PyFlink wheel distribution.

Without this file, type checkers such as mypy treat PyFlink as an untyped package and ignore inline type annotations. Including py.typed makes PyFlink compliant with PEP 561 and enables proper static type checking for users.

---

Brief change log

• Add py.typed to the pyflink package
• Update MANIFEST.in to ensure py.typed is packaged correctly

---

Verifying this change

This change is a trivial packaging fix and can be verified as follows:

• Build the wheel:

  python setup.py bdist_wheel

• Verify py.typed is included:

  unzip -l dist/*.whl | grep py.typed

• Install the package and run mypy on a project importing pyflink to confirm it is no longer treated as untyped.

Same for the sdist:

• Build the sdit:

  python setup.py sdit

• Verify py.typed is included:

  tar xvfz dist/*.tar.g | grep py.typed

No additional tests are required.

---

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery (JobManager, Checkpointing, Kubernetes/Yarn, ZooKeeper): no
• The S3 file system connector: no

---

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

[flinkbot]

CI report:

• 6ff9e70 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[spuru9]

1 minor nit. LGTM

[spuru9]

nit: may consider adding 'py.typed' to PACKAGE_DATA['pyflink'] in setup.py (README.txt precedent)