Unify test cluster infrastructure across Rust and Cpp

[fresh-borzoni]

Search before asking

• 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.

C++ via CXX, watch out for async/sync boundary and generics limitations, it's not trivial

Willingness to contribute

• I'm willing to submit a PR!

[fresh-borzoni]

I decided to split cpp and python, as cpp would be non-trivial, python should be mostly mechanical