Expand Python SDK test coverage

[slbotbm]

Description

Today, the python test suite covers basic happy paths for connectivity, stream/topic creation, polling, TLS, and a few error cases, but it does not exercise the Python binding layer broadly or systematically. There is also no property-based testing, and thus invariants around payload conversion, polling strategy construction, auto-commit configuration, and connection-string parsing are not being stress-tested across a wide input space.

We should strengthen the Python SDK test suite so it can catch binding regressions, input-handling bugs, and edge cases earlier.

Component

Python SDK

Proposed solution

1. Add property-based testing support to foreign/python test dependencies.
   • Add hypothesis to the testing extras in foreign/python/pyproject.toml.
2. Add broader tests for Python-exposed API behavior.
   • Cover valid and invalid inputs, boundary values, Unicode payloads, binary payloads, empty payloads, large payloads, and malformed connection strings.
3. Add property-based tests for binding invariants.
4. Expand the existing suite instead of only adding more happy-path tests.

This work will be done in multiple PR's instead of a single one since the change is large.

Alternatives considered

No response

[slbotbm]

If a contributor wants to pick this up, please state your plan, and how would you go about completing the required changes.

If nobody picks this up, I will in a few days.

tags: python, good first issue, testing