feat: source-transformer for pynumaflow-lite

[vigith]

Closes #267

(pynumaflow-lite) ➜  pynumaflow-lite git:(source-transformer) ✗ pytest tests/test_sourcetransform.py -v 2>&1
================================================================================================= test session starts =================================================================================================
platform darwin -- Python 3.13.2, pytest-8.4.2, pluggy-1.6.0 -- /Users/vigith/code/git/numaproj/numaflow-python/packages/pynumaflow-lite/.venv/bin/python3
cachedir: .pytest_cache
rootdir: /Users/vigith/code/git/numaproj/numaflow-python/packages/pynumaflow-lite
configfile: pyproject.toml
collected 1 item

tests/test_sourcetransform.py::test_python_server_and_rust_client[sourcetransform_event_filter.py] PASSED                                                                                                       [100%]

================================================================================================== 1 passed in 1.02s ==================================================================================================
(pynumaflow-lite) ➜  pynumaflow-lite git:(source-transformer) ✗

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.88%. Comparing base (62f698b) to head (898464c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #293   +/-   ##
=======================================
  Coverage   93.88%   93.88%           
=======================================
  Files          66       66           
  Lines        3009     3009           
  Branches      155      155           
=======================================
  Hits         2825     2825           
  Misses        134      134           
  Partials       50       50           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.