Bootstrap for test suites

Invoke pg_embedded_setup_unpriv::bootstrap_for_tests() in integration suites when both the prepared filesystem layout and the resulting settings are needed. The helper performs the same orchestration as the CLI entry point but returns a TestBootstrapSettings struct containing the final postgresql_embedded::Settings and the environment variables required to exercise the cluster.

use pg_embedded_setup_unpriv::{bootstrap_for_tests, TestBootstrapSettings};
use pg_embedded_setup_unpriv::error::BootstrapResult;

fn bootstrap() -> BootstrapResult<TestBootstrapSettings> {
    let prepared = bootstrap_for_tests()?;
    for (key, value) in prepared.environment.to_env() {
        match value {
            Some(value) => std::env::set_var(&key, value),
            None => std::env::remove_var(&key),
        }
    }
    Ok(prepared)
}

bootstrap_for_tests() ensures that PGPASSFILE, HOME, XDG_CACHE_HOME, XDG_RUNTIME_DIR, and TZ are populated with deterministic defaults. When a timezone database can be discovered (currently on Unix-like hosts) the helper also sets TZDIR; otherwise it leaves any caller-provided value untouched so platform-specific defaults remain available. If the system timezone database is missing, the helper returns an error advising the caller to install tzdata or set TZDIR explicitly, making the dependency visible during test startup rather than when PostgreSQL launches.