ClickHouseRawResult.ReadAsStringAsync (and friends) should support cancellation

### Use case

I want to be able to cancel calls like `rawResult.ReadAsStringAsync()`.

### Describe the solution you'd like

The usual: take an optional `CancellationToken` as a parameter:

```cs
var x = await rawResult.ReadAsStringAsync(cancellationToken)
```

This is not the case currently:

https://github.com/ClickHouse/clickhouse-cs/blob/dd51bfe82a03f0cd47bba74079d288ac8423d347/ClickHouse.Driver/ADO/Readers/ClickHouseRawResult.cs#L120-L124

Note: the cancellationToken passed to `ExecuteRawResultAsync` does not carry over to reads from the returned `ClickHouseRawResult`. Maybe the docs should warn about it.

### Workaround

Not ideal, but sometimes is acceptable.

```cs
var stream = await rawResult.ReadAsStreamAsync();
using (reader = new StreamReader(stream)) {
return await reader.ReadToEndAsync(cancellationToken)
}
```

Start with ClickHouse.Driver/ADO/Readers/ClickHouseRawResult.cs at the referenced lines around ReadAsStringAsync, then inspect the related async read methods and ExecuteRawResultAsync. Confirm how cancellation is currently handled between execution and reads. Done means the relevant read methods accept an optional CancellationToken and the documentation addresses whether execution cancellation carries over.

Written by the indexing model from the issue text.