ci: increase timeouts for slow CLI integration tests

[decofe]

Summary

• increase nextest slow-timeout for CLI integration tests that timed out on slower Windows, macOS, and ARM runners
• keep existing runners, filters, retries, and flaky workflow unchanged

Testing

• uv run python -c "import tomllib; tomllib.load(open('.config/nextest.toml','rb')); print('nextest TOML parsed')"
• git diff --check
• cargo nextest list --locked --workspace --no-run --message-format short (not run: cargo-nextest is not installed in this sandbox)

Prompted by: @grandizzy