IGNITE-27833 [ducktests] Add Multi-DC Integration Test for Cross-DC Network Partition Resilience

[maksaska]

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[anton-vinogradov]

Reviewed the whole PR. The netem/iptables layering (tcset baseline + per-pair DROP chains, so healing is a pure chain flush) is nicely designed, and the tests read well. A few findings below, most with one-line fixes; the two control_utility.py ones and the connect_timeout default affect shared infrastructure beyond MDC.

Nits not tied to a diff line:

• modules/ducktests/tests/tox.ini envlist still contains py38, while the workflow dropped it and tcconfig==0.30.1 requires Python >= 3.9 — a local tox run will fail on the py38 env. Worth removing it there too.
• thin_client_test.py reserves @cluster(num_nodes=8) but allocates 7 (2+2 servers, 1 runner, 2 thin clients).