add query settings injection with OpenTelemetry trace context

[ancieg]

This change lets the driver pass ClickHouse query settings through the client.

That's needed for distributed tracing. If you set a W3C traceparent value in ClientOptions.settings (key opentelemetry_traceparent), the driver copies it into the native protocol OpenTelemetry field so ClickHouse will nest query spans under the existing trace.

• ClientOptions: new settings field (IndexMap<String, String>), defaults to empty so ClientOptions::default() behaviour is unchanged.
• query_raw and insert_native_raw: new third argument query_settings: Option<IndexMap<String, String>> for per-query overrides (pass None to keep defaults).
• No other APIs (query, execute, insert_native, etc.) are changed.

Example:

let mut opts = ClientOptions::default();
opts.settings.insert(
    "opentelemetry_traceparent".into(),
    "00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01".into(),
);
opts.settings.insert("log_comment".into(), "my-service".into());
let client = Client::connect("127.0.0.1:9000", opts).await?;

// These pick up defaults automatically
client.execute("SELECT 1").await?;
client.query_collect::<MyRow>("SELECT * FROM t").await?;

// Per-query override
let overrides: IndexMap<String, String> =
    [("log_comment".into(), "adhoc".into())].into_iter().collect();
client.query_raw("SELECT 2", Some(overrides)).await?;