Add Toxiproxy fault testing

[ruslandoga]

Summary

• add Toxiproxy to the local Compose stack and GitHub Actions services
• add isolated proxy helpers to the current Ch.Test support module
• verify that in-flight normal and multipart queries recover across repeated proxy outages
• observe each disconnect and reconnect directly through DBConnection listeners

Why

The existing low-level fault tests precisely exercise individual HTTP failure paths. This adds complementary end-to-end coverage through a real network proxy, including repeated outages on the same client connection.

Test behavior

Toxiproxy is only contacted by the Toxiproxy fault test. Unrelated test files can still run with ClickHouse alone. To run the complete suite:

docker compose up -d

Validation

• CH_DATABASE=ch_bishkek_toxiproxy_test MIX_ENV=test mix test --include slow — 626 passed, 10 skipped
• CH_DATABASE=ch_bishkek_toxiproxy_test MIX_ENV=test mix test test/ch/faults_test.exs — 28 passed
• MIX_ENV=test mix test test/ch/types_test.exs with Toxiproxy stopped — 171 passed
• MIX_ENV=test mix compile --warnings-as-errors
• MIX_ENV=test mix format
• git diff --check