Unify test cluster infrastructure between Rust and python

[fresh-borzoni]

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• I searched in the issues and found nothing similar.

Description

Test cluster setup is duplicated in three places:

Rust: testcontainers-rs (async, builder pattern)
C++: raw docker run shell commands with TCP polling
Python: testcontainers Python library (sync, pytest fixture)
All three duplicate constants (image name, version, ports, network), orchestration logic (create network, ZK, coordinator, tablet server, wait, and cluster config.

Python could reuse the Rust cluster manager via PyO3 relatively easily (opaque #[pyclass] wrapper, async already supported).

Willingness to contribute

• I'm willing to submit a PR!

[fresh-borzoni]

Good first issue