Support pure synchronous APIs

This is a feature request: Support pure synchronous APIs. The pure means no wrap on top asynchronous APIs. The support may come from various ways:

* Feature flag of the current crate `clickhouse = { version = "x.y.z", features = ["sync"] }`.
* An other crate `clickhouse_sync = { version = "x.y.z" }`.

Maintaining both synchronous and asynchronous APIs must be a hassle in Rust. Are there any chances in the near future?

Start by reviewing the current clickhouse crate's asynchronous API and feature configuration. Compare the two proposed directions: a sync feature in the existing crate or a separate clickhouse_sync crate. Done means providing a pure synchronous API without wrapping asynchronous APIs, with the chosen packaging approach defined.

Written by the indexing model from the issue text.